High-toughness long-lasting heat-resistant alloy for 700 DEG C ultra-supercritical steam turbine rotor and preparation method and application of high-toughness long-lasting heat-resistant alloy

Abstract

The invention relates to a high-toughness long-lasting heat-resistant alloy for a 700-DEG C ultra-supercritical steam turbine rotor and a preparation method and application of the high-toughness long-lasting heat-resistant alloy, and belongs to the technical field of heat-resistant alloys. The high-toughness long-lasting heat-resistant alloy comprises 0.03%-0.05% of C, 17.5%-19.5% of Cr, 6.0%-7.0% of Mo, 13.5%-15.5% of Co, 0.90%-1.20% of Al, 1.40%-1.60% of Ti, 0.30%-0.50% of Nb, 20 ppm-50 ppm of B, smaller than or equal to 0.003% of Mg, smaller than or equal to 0.002% of Zr, smaller than or equal to 0.15% of Si, smaller than or equal to 0.002% of S, smaller than or equal to 0.005% of P, smaller than or equal to 0.70% of Fe, smaller than 0.10% of W and the balance Ni. The heat-resistant alloy not only has higher strength and toughness at room temperature, but also has higher strength and toughness at 700 DEG C.

Description

Technical Field

[0001] This invention relates to the field of heat-resistant alloy technology, and in particular to a high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors, its preparation method, and its application. Background Technology

[0002] With societal development, the demand for electricity is increasing. Thermal power generation is currently the most popular method of power generation. To improve thermal efficiency, the most effective approach is to increase the steam temperature and pressure of the unit. However, as steam temperature and pressure rise, ultra-supercritical generator units place higher demands on the relevant heat-resistant materials.

[0003] Currently, the materials used in 700℃ ultra-supercritical generator sets are mainly nickel-based heat-resistant alloys. One type is solid solution-strengthened alloys, such as Inconel 617B; the other type is age-hardening alloys, such as Nimonic 263. However, while both types of alloys can meet the overall strength requirements, their toughness and high-temperature creep strength are relatively poor. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a high-toughness, long-term durability heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors, its preparation method, and its application, in order to solve the problems of low toughness and insufficient durability fracture time of nickel-based heat-resistant alloys used in 700℃ ultra-supercritical generator sets.

[0005] On the one hand, the present invention provides a high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors. Its chemical composition, by mass percentage, includes C: 0.03~0.05%, Cr: 17.5~19.5%, Mo: 6.0~7.0%, Co: 13.5~15.5%, Al: 0.90~1.20%, Ti: 1.40~1.60%, Nb: 0.30~0.50%, B: 20~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

[0006] Furthermore, its chemical composition, by mass percentage, includes C: 0.03~0.05%, Cr: 17.5~18.5%, Mo: 6.5~7.0%, Co: 14.5~15.5%, Al: 0.90~1.10%, Ti: 1.40~1.50%, Nb: 0.30~0.50%, B: 30~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

[0007] Furthermore, the mass ratio of Co / Mo in the chemical composition of the heat-resistant alloy is 2.1 ≤ Co / Mo ≤ 2.3, and the mass ratio of (Ti+Nb) / C is (Ti+Nb) / C > 35.

[0008] Furthermore, the heat-resistant alloy has a multiphase structure consisting of a face-centered cubic γ matrix, a γ' phase, and carbides; the grain size of the heat-resistant alloy is grade 2 to 6.

[0009] Furthermore, at room temperature, the heat-resistant alloy has a tensile strength Rm ≥ 1050 MPa and a yield strength Rp 0 .2 ≥600MPa, elongation A≥30%, reduction of area Z≥45%, impact energy KV2≥100J.

[0010] Furthermore, at 700℃, the tensile strength Rm of the heat-resistant alloy is ≥850MPa, and the yield strength Rp is ≥850MPa. 0 .2 ≥520MPa, elongation A≥40%, reduction of area Z≥45%, impact energy KV2≥100J; At 700℃ / 400MPa, the time to permanent fracture of the heat-resistant alloy is ≥800h.

[0011] On the other hand, the present invention provides a method for preparing a high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors, comprising the following steps: S1: The ingot is obtained by smelting using the VIM+ESR+VAR triple process or the VIM+ESR double process and then casting. S2: Homogenize the obtained ingot; S3: After homogenization, it undergoes forging and heat treatment to obtain a heat-resistant alloy.

[0012] Furthermore, in step S2, the homogenization treatment temperature is 1180~1200℃, and the holding time is 60~160h.

[0013] Furthermore, in step S3, the heat treatment includes solution treatment and pre-aging treatment; The solution treatment temperature is 1090~1140℃, and the solution is kept at this temperature for 1~3 hours before water cooling. The pre-aging treatment is carried out at a temperature of 720~750℃, and after holding at this temperature for 25~30 hours, it is air-cooled.

[0014] Furthermore, the heat-resistant alloy obtained by this invention can be used to prepare ultra-supercritical steam turbine rotors at 700℃.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. In this invention, through the synergistic interaction of elements and strict control of the content of each element, the resulting heat-resistant alloy exhibits high strength and toughness not only at room temperature but also at 700°C. At room temperature, the tensile strength Rm of the heat-resistant alloy is ≥1050MPa, and the yield strength Rp is... 0 .2 ≥600MPa, elongation A≥30%, reduction of area Z≥45%, impact energy KV2≥100J. At 700℃, the tensile strength Rm≥850MPa and yield strength Rp of the heat-resistant alloy are... 0 .2 The heat-resistant alloy has a strength of ≥520MPa, elongation A≥40%, reduction of area Z≥45%, and impact energy KV2≥100J. Most importantly, the obtained heat-resistant alloy also has high high-temperature creep strength. At 700℃ / 400MPa, the creep fracture time of the heat-resistant alloy is ≥800h.

[0016] 2. The preparation method of this invention employs a VIM+ESR(+VAR) melting process to ensure high purity; a clear homogenization treatment (1180~1200℃ / 60~160h) and graded heat treatment (solution + pre-aging) system is established. These processes effectively eliminate segregation, control grain size (2~6 levels), and enable the alloy to form a multiphase structure (γ matrix + γ' phase + carbides), thereby improving the toughness and creep rupture time of the obtained heat-resistant alloy.

[0017] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0018] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 Metallographic image for grain size rating of embodiment #2; Figure 2 SEM image of carbides after heat treatment in Example 2; Figure 3 The image shows the SEM image of the γ' phase after heat treatment in Example 2#. Detailed Implementation

[0019] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0020] With societal development, the demand for electricity is increasing. Thermal power generation is currently the most popular method of power generation. To improve thermal efficiency, the most effective approach is to increase the steam temperature and pressure of the unit. However, as steam temperature and pressure rise, ultra-supercritical generator units place higher demands on the relevant heat-resistant materials.

[0021] Currently, the materials used in 700℃ ultra-supercritical generator sets are mainly nickel-based heat-resistant alloys. One type is solid solution-strengthened alloys, such as Inconel 617B; the other type is age-hardening alloys, such as Nimonic 263. However, while both types of alloys can meet the overall strength requirements, their toughness and high-temperature creep strength are relatively poor.

[0022] Therefore, this invention provides a high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors. Its chemical composition, by mass percentage, includes C: 0.03~0.05%, Cr: 17.5~19.5%, Mo: 6.0~7.0%, Co: 13.5~15.5%, Al: 0.90~1.20%, Ti: 1.40~1.60%, Nb: 0.30~0.50%, B: 20~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

[0023] Compared with existing technologies, this invention, through the synergistic effect of elements and strict control of their content, yields a heat-resistant alloy that exhibits high strength and toughness not only at room temperature but also at 700°C. At room temperature, the tensile strength Rm of the heat-resistant alloy is ≥1050 MPa, and the yield strength Rp is... 0 .2 ≥600MPa, elongation A≥30%, reduction of area Z≥45%, impact energy KV2≥100J. At 700℃, the tensile strength Rm≥850MPa and yield strength Rp of the heat-resistant alloy are... 0 .2The heat-resistant alloy has a strength of ≥520MPa, elongation A≥40%, reduction of area Z≥45%, and impact energy KV2≥100J. Most importantly, the obtained heat-resistant alloy also has high high-temperature creep strength. At 700℃ / 400MPa, the creep fracture time of the heat-resistant alloy is ≥800h.

[0024] The functions of each element are as follows: Carbon: The amount of carbon added in nickel-based heat-resistant alloys affects the types of carbides formed, including MC and M. 23 There are three types of carbides: C6, M6C, and M6C. Among them, MC-type carbides have the highest thermal stability. Stable and fine MC-type carbide particles effectively pin grain boundaries, hindering slip and dislocation movement, and are the cornerstone of high-temperature creep resistance. M6C-type carbides are metastable phases and have the worst thermal stability among the three carbides. They are prone to transforming into brittle TCP phases (σ, μ), leading to a catastrophic decrease in creep performance. 23 C6 type carbides are intermediate-temperature stable secondary phases that can be formed from MC type and M6C type carbides. Granular M6C carbides are formed from fine MC type carbides. 23 C6-type carbides can pin grain boundaries, which is beneficial to intermediate-temperature creep strength, while M6-type carbides are transformed from M6C-type carbides. 23 C6 type carbides often inherit the distribution morphology of M6C, with M6C distributed in a continuous thin film. 23 C6 is detrimental to plasticity and lifespan; therefore, the present invention strictly controls the C content to 0.03~0.05%, and further controls the Ti+Nb content to generate fine MC-type primary carbides.

[0025] Chromium: The resistance of heat-resistant alloys to steam corrosion increases with increasing Cr content. However, excessive Cr promotes the formation of long-term harmful σ phase, and the precipitation of σ phase will act as a creep crack initiation point, reducing creep strength. Therefore, in order to meet the requirements of steam corrosion resistance and control of long-term harmful σ phase, the Cr content is controlled at 17.5~19.5%.

[0026] Molybdenum: The atomic radius of Mo is much larger than that of nickel. When it is dissolved in the face-centered cubic γ matrix of nickel, it causes severe lattice distortion and generates a strong stress field. This stress field can effectively hinder dislocation movement and significantly improve the strength, hardness and creep resistance of heat-resistant alloys.

[0027] Mo is a strong carbide-forming element with a high electron vacancy concentration. Adding Mo to an alloy increases the average electron vacancy concentration of the alloy matrix, which is conducive to the formation of M6C-type carbides. Therefore, excess Mo preferentially combines with carbon to form molybdenum-rich M6C-type carbides. Furthermore, adding too much Mo significantly increases the alloy's susceptibility to weld cracking. To avoid the formation of primary M6C-type carbides during solidification and their transformation into harmful phases during service, thus reducing weld cracking susceptibility, the Mo content in the heat-resistant alloy of this invention is strictly controlled at 6.0–7.0%.

[0028] Cobalt (Co) is also a solid solution strengthening element. Appropriate amounts of Co reduce the stacking fault energy of the matrix, promote plane slip of dislocations while inhibiting climb, increase the dissolution temperature of the γ' phase, improve the high-temperature stability of the γ' phase, inhibit TCP phase precipitation, and improve the plasticity and toughness of the alloy. Co has a low electron vacancy concentration; the addition of Co reduces the average electron vacancy concentration of the alloy matrix, inhibits the precipitation of metastable M6C-type carbides, and promotes the precipitation of MC-type carbides. However, excessive Co can form harmful intermetallic compounds (μ phases). Therefore, the Co content in this invention is controlled at 13.5% to 15.5%.

[0029] Preferably, the Co / Mo mass ratio is controlled between 2.1 and 2.3.

[0030] Aluminum: The core role of Al is to form the strengthening phase γ'-Ni3Al. The γ' phase effectively hinders dislocation movement, and its strength increases with temperature, thereby improving high-temperature strength. Aluminum selectively oxidizes at high temperatures, forming a dense and strongly adhering Al2O3 protective film on the alloy surface. However, when welding alloys with high aluminum content, the low-melting-point eutectic liquid film formed at the end of weld metal solidification and the high tendency for hot cracking deteriorate their weldability. Therefore, the Al content in the alloy of this invention ranges from 0.90% to 1.20%.

[0031] Titanium: Ti is the main forming element of the γ′ phase. Titanium can partially replace aluminum atoms in the γ′ phase to form Ni3(Al,Ti). The solubility of titanium in the γ matrix is ​​much higher than that in the γ′ phase, so adding titanium will significantly increase the volume fraction of the γ′ phase. Titanium and niobium have a strong affinity for carbon and nitrogen and can form stable MC-type carbonitrides. When the (Ti+Nb) / C mass ratio is high, it can promote the refinement of the MC phase. However, titanium is a strong TCP phase (σ, μ phase) forming element. Excessive titanium will significantly reduce the stacking fault energy of the alloy and increase the electron-hole concentration, thereby greatly promoting the precipitation of these plate-like or needle-like brittle phases at grain boundaries during long-term high-temperature service, deteriorating the alloy performance. Therefore, based on the control of γ′ phase content, long-term harmful phases, and carbide morphology, the alloy of this invention controls the Ti content at 1.40~1.60% and the Ti+Nb to C mass ratio at >35.

[0032] Niobium (Nb) is an extremely strong γ′ phase-forming element. It can dissolve extensively into the γ′ phase, partially replacing aluminum and titanium to form Ni3(Al, Ti, Nb). The addition of niobium significantly improves the lattice mismatch and antiphase domain boundary energy of the γ′ phase. Niobium is also a strong carbide-forming element, preferentially forming MC-type carbides. Fine MC carbides within the grain can pin dislocations, providing some strengthening. More importantly, during heat treatment or service, MC carbides decompose, generating fine M-type carbides at the grain boundaries. 23 C6 carbide chains. This chain-like structure effectively pins grain boundaries, inhibits grain boundary sliding and migration, significantly improves the alloy's creep strength and ductility, but excessive Nb can lead to segregation, Laves phase formation, deterioration of weldability and ductility, and promotes the precipitation of brittle TCP phases such as σ / μ, thus worsening long-term stability. Therefore, the Nb content in the alloy of this invention is controlled within the range of 0.30~0.50%.

[0033] Boron: Trace amounts of boron are typically distributed in γ' / M 23 C6 and γ / M 23 At the C6 interface, reducing C segregation towards the grain boundaries effectively strengthens the grain boundaries and inhibits grain boundary slip and void nucleation during creep, which is crucial for the alloy's durability and lifespan. However, when the content exceeds a certain level, the grain boundary strengthening effect no longer increases significantly and it also affects the alloy's weldability. Therefore, the B content in the alloy of this invention is controlled at 20-50 ppm.

[0034] Magnesium (Mg): Mg is chemically highly reactive and has a strong affinity for O and S. It preferentially reacts with trace amounts of harmful impurity element S that segregate at grain boundaries to form stable MgS or MgO·MgS composite compounds, effectively eliminating S segregation at grain boundaries and significantly improving grain boundary cohesion and strength. Simultaneously, Mg segregation at grain boundaries lowers grain boundary energy, transforming continuously precipitated thin-film or blocky carbides into granular forms. These discontinuous, spheroidized precipitates effectively pin grain boundaries, inhibiting grain boundary slippage and avoiding the risk of continuous precipitates acting as rapid crack propagation pathways. This improves the alloy's creep ductility and creep strength, increases grain boundary bonding, and enhances hot strength. However, excessive Mg can form a low-melting-point brittle phase, leading to severe grain boundary embrittlement. Therefore, the Mg content in the alloy of this invention is strictly controlled at ≤0.003%.

[0035] Zirconium: Zr atoms have a large atomic radius and strongly segregate at grain boundaries, purifying them and enhancing grain boundary cohesion. However, excessive Zr content can form low-melting-point intermetallic compounds or eutectic phases with matrix elements such as Ni and Cr at grain boundaries, severely deteriorating room-temperature and intermediate-temperature plasticity and toughness, drastically reducing creep life, and making the alloy unsuitable for hot working and welding. Therefore, the Zr content in the alloy of this invention is controlled at ≤0.002%.

[0036] Silicon: Si forms a low-melting-point eutectic with Ni, which accumulates at grain boundaries, reducing grain boundary strength and impairing hot workability. Similar to P, Si is also a strong promoter of TCP phase formation, deteriorating long-term performance. Therefore, the invented alloy does not contain Si, and the Si content in the furnace charge is limited to less than 0.15%.

[0037] Sulfur: S diffuses readily at high temperatures and strongly segregates at grain boundaries, forming a low-melting-point Ni-Ni3S2 eutectic with Ni, which greatly deteriorates the alloy's hot workability and high-temperature plasticity, and impairs weldability. Therefore, the sulfur content in this alloy needs to be strictly controlled below 0.002%.

[0038] Phosphorus: P is also a strong grain boundary segregating element. The segregation of P significantly reduces the nucleation work of topologically close-packed phases, promotes the precipitation of brittle phases at grain boundaries, and severely weakens grain boundaries. Therefore, the phosphorus content in this alloy must be less than 0.005%.

[0039] Iron: Fe can form harmful phases with elements such as Mo, reducing the alloy's resistance to pitting and crevice corrosion. Therefore, Fe in the alloy of this invention is limited to a low level. Thus, Fe is not added to the alloy of this invention and its content is controlled to within 0.70%.

[0040] Tungsten: W is a strong carbide-forming element, with an electron vacancy concentration close to that of Mo, and directly participates in... The absence of W promotes the formation of MC-type primary carbides, thereby improving the alloy's creep ductility and crack propagation resistance. Tungsten, with its high melting point and low diffusion rate, readily causes microsegregation during weld solidification, promoting the formation of low-melting-point eutectic phases. The W-free alloy exhibits reduced weld crack susceptibility, resulting in excellent weldability. Therefore, the W content in this invention is controlled to below 0.10%.

[0041] Preferably, its chemical composition, by mass percentage, includes C: 0.03~0.05%, Cr: 17.5~18.5%, Mo: 6.5~7.0%, Co: 14.5~15.5%, Al: 0.90~1.10%, Ti: 1.40~1.50%, Nb: 0.30~0.50%, B: 30~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

[0042] Specifically, the heat-resistant alloy has a multiphase structure consisting of a face-centered cubic γ matrix, a γ' phase, and carbides; the grain size of the heat-resistant alloy is grade 3 to 7.

[0043] This invention provides a method for preparing a high-toughness, long-creation heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors, comprising the following steps: S1: The ingot is obtained by smelting using the VIM+ESR+VAR triple process or the VIM+ESR double process and then casting. S2: Homogenize the obtained ingot; S3: After homogenization, it undergoes forging and heat treatment to obtain a heat-resistant alloy.

[0044] It should be noted that the preparation method of this invention employs a VIM+ESR(+VAR) melting process to ensure high purity; and establishes a clear homogenization treatment (1180~1200℃ / 60~160h) and graded heat treatment (solution + pre-aging) system. These processes effectively eliminate segregation, control grain size (3~7 levels), and enable the alloy to form a multiphase structure (γ matrix + γ' phase + carbides), thereby improving the toughness and creep rupture time of the resulting heat-resistant alloy.

[0045] Specifically, in step S2, the homogenization treatment temperature is 1180~1200℃, and the holding time is 60~160h.

[0046] It should be noted that when the temperature exceeds 1200℃, the alloy ingot will exhibit oxidation and peeling, resulting in pitting or corrosion on its surface; while when the temperature is too low, the diffusion process is insufficient, and microsegregation cannot be effectively eliminated. Although this can be improved by using low-temperature, long-term diffusion, the required time will increase exponentially.

[0047] Specifically, in step S3, the heat treatment includes solution treatment and pre-aging treatment; The solution treatment temperature is 1090~1140℃, and the solution is kept at this temperature for 1~3 hours before water cooling. The pre-aging treatment is carried out at a temperature of 720~750℃, and after holding at this temperature for 25~30 hours, it is air-cooled.

[0048] It should be noted that solution treatment is performed within this temperature range, which is higher than the complete dissolution temperature of the γ' phase in the alloy. This ensures that the vast majority of the γ' phase falls back into the matrix, forming a uniform supersaturated solid solution. This is a prerequisite for obtaining fine, uniform γ' phases through subsequent aging treatment. Pre-aging treatment at 720~750℃ not only yields fine, uniform, and thermally stable γ' phases and carbides, but also improves the toughness and creep strength of the heat-resistant alloy.

[0049] In this invention, the solution treatment temperature can be 1090℃, 1100℃, 1110℃, 1120℃, 1130℃ or 1140℃.

[0050] The temperature for the pre-aging treatment can be 720℃, 730℃, 740℃ or 750℃.

[0051] Specifically, the heat-resistant alloy obtained by this invention is used to prepare ultra-supercritical steam turbine rotors at 700℃.

[0052] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0053] Example 1 The preparation process of heat-resistant alloys includes the following steps: S1: The VIM+ESR+VAR triple process is used for smelting, and the ingot is obtained after casting. S2: The obtained ingot is homogenized; the homogenization temperature is 1200℃ and the holding time is 100h.

[0054] S3: After homogenization treatment, it is forged and heat treated to obtain a heat-resistant alloy. The heat treatment includes solution treatment and pre-aging treatment; The solution treatment temperature is 1100℃, and after holding at that temperature for 2 hours, it is water cooled. The pre-aging treatment was carried out at a temperature of 720°C for 30 hours, followed by air cooling.

[0055] The chemical compositions of the heat-resistant alloys obtained in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0056]

[0057] Notes: 1# is the heat-resistant alloy obtained in Example 1 of this invention; 2# is the heat-resistant alloy obtained in Example 2 of this invention; 3# is the heat-resistant alloy obtained in Example 3 of this invention; 4# is the heat-resistant alloy obtained in Comparative Example 1 of this invention, and its grade is C700R-1; 5# is the heat-resistant alloy obtained in Comparative Example 2 of this invention, and its grade is Nimonic 263; 6# is the heat-resistant alloy obtained in Comparative Example 3 of this invention, and its grade is TOSIX-Ⅱ.

[0058] Performance testing The above embodiments and comparative examples were subjected to performance tests, mainly including mechanical properties at room temperature and high temperature. The test results are shown in Tables 2-4.

[0059] Table 2 Performance test results at room temperature

[0060] Table 3 Performance test results at 700℃

[0061] Table 4 Results of Duration Fracture Time Test

[0062] In conjunction with Examples 1-3 and Comparative Examples 1-3, and referring to Tables 2-4, and in combination with... Figure 1-3 As can be seen, in this invention, through the synergistic effect between elements and strict control of the content of each element, the resulting heat-resistant alloy not only exhibits high strength and toughness at room temperature, but also at 700℃. At room temperature, the tensile strength Rm of the heat-resistant alloy is ≥1050MPa, and the yield strength Rp is... 0 .2 ≥600MPa, elongation A≥30%, reduction of area Z≥45%, impact energy KV2≥100J. At 700℃, the tensile strength Rm≥850MPa and yield strength Rp of the heat-resistant alloy are... 0 .2 The heat-resistant alloy has a strength of ≥520MPa, elongation A≥40%, reduction of area Z≥45%, and impact energy KV2≥100J. Most importantly, the obtained heat-resistant alloy also has high high-temperature creep strength. At 700℃ / 400MPa, the creep fracture time of the heat-resistant alloy is ≥800h.

[0063] Figure 1 The image shows the grain size rating of alloy #2 after 1100℃×2h water cooling process. The average grain size level is 5.6.

[0064] Figure 2 SEM image of carbides after heat treatment of alloy #2 at 1100℃ for 2 hours, followed by water cooling at 720℃ for 30 hours, and air cooling. A small amount of granular Ti-rich carbides are dispersed within the grains and at the grain boundaries.

[0065] Figure 3 The image shows the SEM image of the γ' phase after heat treatment of alloy #2 at 1100℃ for 2 hours, followed by water cooling at 720℃ for 30 hours, and then air cooling. The γ' phase is smaller than 25 nm in size and is uniformly distributed.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors, characterized in that, Based on mass percentage, its chemical composition includes C: 0.03~0.05%, Cr: 17.5~19.5%, Mo: 6.0~7.0%, Co: 13.5~15.5%, Al: 0.90~1.20%, Ti: 1.40~1.60%, Nb: 0.30~0.50%, B: 20~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

2. The high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 1, characterized in that, The chemical composition, by mass percentage, includes C: 0.03~0.05%, Cr: 17.5~18.5%, Mo: 6.5~7.0%, Co: 14.5~15.5%, Al: 0.90~1.10%, Ti: 1.40~1.50%, Nb: 0.30~0.50%, B: 30~50ppm, Mg≤0.003%, Zr≤0.002%, Si≤0.15%, S≤0.002%, P≤0.005%, Fe≤0.70%, W<0.10%, with the balance being Ni and unavoidable impurity elements.

3. The high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 1 or 2, characterized in that, The heat-resistant alloy has the following chemical composition: Co / Mo mass ratio: 2.1 ≤ Co / Mo ≤ 2.3, (Ti+Nb) / C mass ratio: (Ti+Nb) / C > 35.

4. The high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 1, characterized in that, The heat-resistant alloy has a multiphase structure consisting of a face-centered cubic γ matrix, a γ' phase, and carbides; the grain size of the heat-resistant alloy is grade 2 to 6.

5. The high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 1, characterized in that, At room temperature, the tensile strength Rm of the heat-resistant alloy is ≥1050MPa, and the yield strength Rp is ≥1050MPa. 0 .2 ≥600MPa, elongation A≥30%, reduction of area Z≥45%, impact energy KV2≥100J.

6. The high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 1, characterized in that, At 700℃, the tensile strength Rm of the heat-resistant alloy is ≥850MPa, and the yield strength Rp is ≥850MPa. 0 .2 ≥520MPa, elongation A≥40%, reduction of area Z≥45%, impact energy KV2≥100J; At 700℃ / 400MPa, the time to permanent fracture of the heat-resistant alloy is ≥800h.

7. A method for preparing a high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotors as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: The ingot is obtained by smelting using the VIM+ESR+VAR triple process or the VIM+ESR double process and then casting. S2: Homogenize the obtained ingot; S3: After homogenization, it undergoes forging and heat treatment to obtain a heat-resistant alloy.

8. The method for preparing the high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 7, characterized in that, In step S2, the homogenization treatment temperature is 1180~1200℃, and the holding time is 60~160h.

9. The method for preparing the high-toughness, long-lasting heat-resistant alloy for 700℃ ultra-supercritical steam turbine rotor according to claim 7, characterized in that, In step S3, the heat treatment includes solution treatment and pre-aging treatment; The solution treatment temperature is 1090~1140℃, and after holding at this temperature for 1~3 hours, it is water-cooled. The pre-aging treatment is performed at a temperature of 720~750℃, and the temperature is maintained for 25~30 hours before air cooling.

10. The application of the heat-resistant alloy according to any one of claims 1-6 or the heat-resistant alloy obtained by the preparation method according to any one of claims 7-9 in the preparation of a 700℃ ultra-supercritical steam turbine rotor.

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