Nickel-based rotor forging of 650 DEG C ultra-supercritical steam turbine and heat treatment method of nickel-based rotor forging

Abstract

The invention relates to a 650 DEG C ultra-supercritical steam turbine nickel-based rotor forge piece and a heat treatment method thereof, and belongs to the technical field of heat treatment methods. The heat treatment method of the nickel-based rotor forging comprises solution treatment and two-step aging treatment, the temperature of the solution treatment is 1100-1160 DEG C, the heat preservation time is 1-1.5 h / 100 mm, and water cooling is carried out; the aging temperature in the first step is 720-750 DEG C, the heat preservation time is 24-30 h, and air cooling is carried out; the aging temperature in the second step is 660-700 DEG C, the heat preservation time is 48-72 hours, and air cooling is carried out. The obtained rotor forging has high room temperature and high temperature performance, and at the room temperature, the tensile strength is 912 MPa or above, and the yield strength is 483 MPa or above. And at the temperature of 650 DEG C, the tensile strength is 786 MPa or above, and the yield strength is 408 MPa or above. The extrapolated endurance strength at 650 DEG C / 105h is greater than or equal to 240MPa.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment methods, and in particular to a 650°C ultra-supercritical steam turbine nickel-based rotor forging and a heat treatment method thereof. Background Art

[0002] Ultra-supercritical steam turbine rotors need to withstand 650℃ / 30~35MPa flowing steam erosion and a speed of up to 3000 rpm during service. Therefore, ultra-supercritical steam turbine rotors are required to have good room temperature and high temperature strength, long-lasting creep performance, and good resistance to high temperature steam oxidation.

[0003] Martensitic heat-resistant steel is a common material for making rotor forgings, but its service temperature cannot reach 650°C, so it is gradually replaced by nickel-based heat-resistant alloys. In order to improve the performance of nickel-based heat-resistant alloys or turbine rotor forgings, the main focus is on alloy composition ratios and heat treatment methods. At present, the heat treatment methods used are solution treatment and aging treatment. However, the existing treatment process has limited performance improvement and cannot guarantee the comprehensive mechanical properties of turbine rotor forgings.

[0004] Therefore, there is an urgent need for a preparation method to improve the comprehensive mechanical properties of ultra-supercritical steam turbine rotors at high temperatures. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a 650°C ultra-supercritical steam turbine nickel-based rotor forging and a heat treatment method thereof to ensure that the ultra-supercritical steam turbine rotor has higher comprehensive mechanical properties at high temperatures.

[0006] In one aspect, the present invention provides a heat treatment method for a 650°C ultra-supercritical steam turbine nickel-based rotor forging, wherein the heat treatment method comprises a solution treatment and a two-step aging treatment.

[0007] The temperature of the solution treatment is 1100-1160°C, the holding time is 1-1.5h / 100mm, and the solution is water-cooled;

[0008] The first step of aging is at a temperature of 720-750°C, with a holding time of 24-30 hours and air cooling;

[0009] The second step of aging is at a temperature of 660-700°C, with a holding time of 48-72 hours and air cooling.

[0010] Furthermore, the temperature of the solution treatment is 1140-1160°C, and the holding time is 1-1.5h / 100mm;

[0011] The first step of aging is at a temperature of 735-750°C and the holding time is 24-30 hours;

[0012] The second step aging temperature is 675-700℃, and the holding time is 48-72h.

[0013] Furthermore, during solution treatment, the temperature is raised to 650-700°C according to the maximum power of the heat treatment furnace, and the uniform heating is carried out at a speed of 1.0-1.5 mm / min; then the temperature is raised to 1000-1050°C at a heating rate of 30-40°C / h, and kept warm for 2-3 hours; finally, the temperature is raised to 1100-1160°C at a heating rate of 15-20°C / h, and kept warm for 6-9 hours before being taken out of the furnace and water-cooled.

[0014] Furthermore, the heating rates of the first aging step and the second aging step are ≤60°C / h.

[0015] Furthermore, the chemical composition of the rotor forging, measured by mass percentage, includes C: 0.05-0.08%, Cr: 21.0-23.0%, Co: 6.5-8.8%, Mo: 6.0-8.8%, Al: 0.70-1.40%, Ti: 0.40-0.80%, Nb: 0.15-0.55%, B: 0.002-0.005%, Zr: 0.015-0.06%, and the remainder is nickel and unavoidable impurity elements.

[0016] Further, the precipitated phase includes M 23 C6 type carbide and γ′ phase.

[0017] Furthermore, the mass fraction of the γ′ phase is 6-8%, M 23 The mass fraction of C6 carbide is above 1%.

[0018] Furthermore, the room temperature yield strength of the rotor forging is ≥480MPa, the high temperature yield strength at 650℃ is ≥320MPa, and the 5 h Extrapolated endurance strength ≥240MPa.

[0019] Furthermore, the cross-sectional size of the rotor forging is 900-1100 mm.

[0020] On the other hand, the present invention provides a 650°C ultra-supercritical steam turbine nickel-based rotor forging, which is prepared by the heat treatment method described in the present invention.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] 1. In the present invention, the forging blank obtained after forging is heat treated. The heat treatment method adopts solution treatment and two aging treatments. By strictly controlling the treatment temperature, holding time, cooling method, etc., the rotor forgings after heat treatment have better performance, room temperature yield strength ≥480MPa, 650℃ high temperature yield strength ≥320MPa, 650℃ / 10 5 h Extrapolated endurance strength ≥240MPa.

[0023] 2. In the rotor forging after heat treatment, the precipitated phase includes M 23 C6 type carbide and γ′ phase, and the mass fraction of the γ′ phase is 6-8%, M 23 The mass fraction of C6 carbide is above 1%.

[0024] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] Figure 1 M in Example 4 23 SEM image of C6 carbide;

[0027] Figure 2 is the SEM image of the γ′ phase in Example 4;

[0028] Figure 3 This is the particle size distribution diagram of the γ′ phase in Example 4. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings 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 used to limit the scope of the present invention.

[0030] The service conditions of ultra-supercritical steam turbine rotors are very harsh. They not only need to withstand high temperature and pressure, but also need to bear high speed. Therefore, ultra-supercritical steam turbine rotors are required to have good room temperature and high temperature strength, long-lasting creep performance, and good resistance to high temperature steam corrosion.

[0031] Nickel-based alloys are alternative materials for preparing 650℃ ultra-supercritical steam turbine rotors. In order to improve the performance of nickel-based heat-resistant alloys or steam turbine rotor forgings, the main focus is on alloy composition ratios and heat treatment methods. At present, the heat treatment methods used are solution treatment and aging treatment. However, the existing treatment process has limited performance improvement and cannot guarantee the comprehensive mechanical properties of steam turbine rotor forgings.

[0032] The existing heat treatment methods mainly use solution treatment and primary aging treatment. Since the ultra-supercritical steam turbine rotor forgings are large in size, with a cross-sectional size of 900 to 1100 mm, in order to ensure that the alloy ingots are fully permeable, the holding time of the solution treatment needs to be extended. However, after extending the solution holding time, it is found that the yield strength of the ultra-supercritical steam turbine rotor forgings is significantly reduced and cannot meet the performance requirements.

[0033] Therefore, in order to ensure the comprehensive mechanical properties of ultra-supercritical steam turbine rotor forgings, the present invention provides a heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings, wherein the heat treatment method comprises a solid solution treatment and a two-step aging treatment.

[0034] The temperature of the solution treatment is 1100-1160°C, the holding time is 1-1.5h / 100mm, and the solution is water-cooled;

[0035] The first step of aging is at a temperature of 720-750°C, with a holding time of 24-30 hours and air cooling;

[0036] The second step of aging is at a temperature of 660-700°C, with a holding time of 48-72 hours and air cooling.

[0037] Compared with the prior art, the present invention adopts a solution treatment and a two-step aging treatment method to heat treat the rotor forging obtained by forging, so that the rotor forging obtains M 23 C6 carbide and γ′ phase ensure that the rotor forging has high comprehensive mechanical properties.

[0038] In the prior art, some nickel-based alloys use a single solution and double aging heat treatment method, which uses a low-temperature solution (below 1030°C) and a high-temperature short-time aging (one aging temperature is above 830°C, and the insulation temperature is less than 10h). This heat treatment method is aimed at alloy systems with multiple strengthening phases and different precipitation temperature ranges of strengthening phases. However, the Al and Ti elements in this alloy system are relatively low, and the types of precipitation phases are relatively small, mainly including γ′ phase and M 23 C6 type carbide, and γ′ phase and M 23 The precipitation temperature range of C6 type carbides is relatively close, and the alloy strength cannot be improved through the existing two-step aging treatment.

[0039] The temperature of the solution treatment of the present invention is controlled at 1100-1160°C, and the holding time is calculated according to the cross-sectional size of the rotor forging, and the holding time is 1-1.5h / 100mm. The solution treatment is to allow the original primary carbides and the carbides precipitated during the forging process to fully dissolve back, and to form uniformly distributed fine granular precipitation during the aging treatment process, pinning the grain boundary migration and dislocation slip, and achieving the effect of precipitation strengthening. Through this solution treatment system, the grain size can be determined to be 1-4 levels.

[0040] When the temperature of the solution treatment is lower than 1100℃, there are a large number of primary carbides that are not completely dissolved, which can easily become crack sources and reduce the durability life; when the temperature of the solution treatment is higher than 1160℃, the rate of grain coarsening increases significantly, which can easily lead to abnormal growth of coarse grains and individual grains.

[0041] Preferably, the temperature of the solution treatment may be 1100°C, 1110°C, 1120°C, 1125°C, 1130°C, 1140°C, 1145°C, 1150°C or 1160°C.

[0042] When formulating the heat treatment system, the thermodynamic and kinetic factors of the alloy need to be comprehensively considered. The present invention adopts a two-step aging treatment method in the aging process. The temperature of the first step aging is 720-750°C, and the holding time is 24-30h. The purpose is to make the carbide and γ′ phase precipitate quickly and close to the equilibrium precipitation amount. The temperature of the second step aging is 660-700°C, and the holding time is 48-72h. The second step aging temperature is lower than the first step aging temperature. After lowering the aging temperature, the difference in the equilibrium precipitation amount of the alloy at different temperatures is used to further precipitate the γ′ phase. The mass fraction of the γ′ phase is above 6%, and M 23 The mass fraction of C6 carbide is about 1% or more, thereby ensuring the comprehensive mechanical properties of the rotor forging.

[0043] The present invention proposes a novel two-step aging treatment method, which comprehensively considers the thermodynamic and kinetic characteristics of the γ′ phase of the alloy system, keeps the temperature in the temperature range of 720-750°C to allow the γ′ phase to precipitate rapidly to the equilibrium precipitation amount within this temperature range, and then reduces the secondary aging temperature to promote further precipitation of the γ′ phase. However, the reduction of the aging temperature will lead to a significant reduction in the precipitation rate of the γ′ phase, and too low an aging temperature will result in the failure to significantly improve the strength of the alloy even if the temperature is kept for a long time.

[0044] Specifically, the precipitated phase includes M 23 C6 type carbide and γ′ phase.

[0045] Preferably, the mass fraction of the γ′ phase is above 6%, and M 23 The mass fraction of C6 carbide is above 1%.

[0046] It should be noted that in the present invention, different temperatures are used for aging, not only M 23 There are two precipitation phases: C6 carbide and γ′ phase. The mass fraction of γ′ phase is above 6%, and the size of γ′ phase is bimodal distribution. The size of γ′ phase is ≤30nm. The small and uniformly distributed γ′ phase can fully exert the precipitation strengthening effect.

[0047] Specifically, the size of the γ′ phase presents a bimodal distribution, mainly concentrated in two peaks of 1-5 nm and 10-18 nm.

[0048] In the present invention, the first aging temperature may be 720°C, 725°C, 730°C, 735°C, 740°C, 745°C or 750°C. When the first aging temperature is lower than 720°C, the γ′ phase and M 23 The precipitation rate of C6 carbides is slow, especially M 23 The mass fraction of C6 carbide is less than 1%, and the alloy strength is low and cannot meet the strength requirements. When the temperature of the first step of aging is higher than 750℃, M 23 The lamellar precipitation of C6 carbide and the lamellar M 23 The interface between C6 and the matrix is ​​prone to cracking, resulting in a decrease in strength.

[0049] In the present invention, the insulation time of the first step of aging can be 24h, 25h, 26h, 28h or 30h.

[0050] In the present invention, the temperature of the second aging step can be 660°C, 670°C, 675°C, 690°C or 700°C. When the temperature of the second aging step is lower than 660°C, due to the low aging temperature, the precipitation rate of the γ′ phase is too slow, and even after a long-term heat preservation of 100 hours, the strength requirement cannot be met. When the temperature of the second aging step is higher than 700°C, the amount of precipitation of the γ′ phase in the equilibrium state increases less than that of the first aging step, and the strengthening effect of the second aging step cannot be fully exerted.

[0051] In the present invention, the insulation time of the second aging step can be 48h, 50h, 55h, 60h, 65h, 70h or 72h.

[0052] Specifically, during solution treatment, the temperature is raised to 650-700°C according to the maximum power of the heat treatment furnace, and the temperature is evenly heated at a speed of 1.0-1.5 mm / min; then the temperature is raised to 1000-1050°C at a heating rate of 30-40°C / h, and kept warm for 2-3 hours; finally, the temperature is raised to 1100-1160°C at a heating rate of 15-20°C / h, and kept warm for 6-9 hours before being taken out of the furnace and water-cooled.

[0053] Specifically, the chemical composition of the rotor forging, by mass percentage, includes C: 0.05-0.08%, Cr: 21.0-23.0%, Co: 6.5-8.8%, Mo: 6.0-8.8%, Al: 0.70-1.40%, Ti: 0.40-0.80%, Nb: 0.15-0.55%, B: 0.002-0.005%, Zr: 0.015-0.06%, and the remainder is nickel and unavoidable impurity elements.

[0054] In the present invention, M is precipitated after heat treatment. 23 C6 carbides and γ′ phase can effectively pin dislocation movement and improve alloy strength. However, they are prone to degradation during long-term service at high temperatures (e.g., 700°C). For precipitation-strengthened nickel-based heat-resistant alloys, this is mainly manifested as the coarsening of the γ′ phase, which can easily lead to a significant decrease in mechanical properties after a period of service. Therefore, this alloy system adopts a design concept that combines solid solution strengthening and precipitation strengthening, and has good mechanical properties and organizational stability.

[0055] The main role of C element in this alloy system is to form M 23 C6 type carbide, carbide has a significant strengthening effect on the short-term mechanical properties of the alloy; Cr element mainly improves the oxidation resistance of the alloy, and is also the main forming element of carbide; Co and Mo are the main solid solution strengthening elements; Al and Ti elements are γ′ phase forming elements. The Al and Ti elements in this alloy system are relatively low, while meeting the mechanical performance requirements of the 650℃ ultra-supercritical steam turbine rotor, it can avoid the deterioration of smelting, forging and welding performance caused by excessive γ′ phase formation. This alloy system has excellent processing and forming properties, and can manufacture rotor forgings with a diameter of more than 1000mm.

[0056] The present invention provides a 650°C ultra-supercritical steam turbine nickel-based rotor forging, which is prepared by the heat treatment method of the present invention. The preparation method comprises the following steps:

[0057] S1: smelting;

[0058] S2: Forging;

[0059] S3: heat treatment, the heat treatment method is solution treatment and two-step aging treatment,

[0060] The temperature of the solution treatment is 1100-1160°C, and the holding time is 1-1.5h / 100mm;

[0061] The first step of aging is at a temperature of 720-750°C and the holding time is 24-30 hours;

[0062] The second step aging temperature is 660-700℃, and the holding time is 48-72h.

[0063] It should be noted that in the present invention, the existing process can be used to prepare the forging blank during the smelting and forging process. For example, in the smelting process, according to the proportion of alloy components, the ingot is smelted by a triple process of vacuum induction melting + protective atmosphere electroslag + vacuum consumable remelting, and then poured and cooled to prepare the ingot. In the forging process, the obtained ingot is forged and blanked, and then forged into a columnar rotor forging. The forging temperature is 1160-1180°C, and the final forging temperature is above 990°C. If the temperature is lower than the final forging temperature during the forging process, it needs to be returned to the furnace for heating before forging.

[0064] Specifically, the cross-sectional size of the rotor forging is 900-1100 mm.

[0065] Specifically, the room temperature yield strength of the rotor forging is ≥480MPa, the high temperature yield strength at 650°C is ≥320MPa, and the 5 h Extrapolated endurance strength ≥240MPa.

[0066] In order to more clearly describe the present invention, it is further illustrated by the following examples and comparative examples.

[0067] Example 1

[0068] The preparation of 650℃ ultra-supercritical steam turbine nickel-based rotor forgings includes the following steps:

[0069] S1: The smelting process adopts vacuum induction melting + protective atmosphere electroslag + vacuum consumable remelting triple process smelting, and the chemical composition of the obtained ingot is C: 0.064%, Cr: 21.69%, Co: 8.32%, Mo: 7.15%, Al: 1.04%, Ti: 0.51%, Nb: 0.20%, B: 0.0041%, Zr: 0.036%, and the balance is nickel;

[0070] S2: forging; heating the obtained ingot, controlling the start forging temperature to be 1170±5°C, and the final forging temperature to be 990°C, to obtain a forging blank;

[0071] S3: the forging blank is divided and heat treated under different conditions to obtain an ultra-supercritical steam turbine nickel-based rotor forging with a cross-section of 1000 mm; the heat treatment method is a solid solution treatment and a two-step aging treatment,

[0072] The temperature of the solution treatment is 1120-1160°C, and the holding time is 1-1.5h / 100mm;

[0073] The first step of aging is at a temperature of 720-750°C and the holding time is 24-30 hours;

[0074] The second step aging temperature is 660-700℃, and the holding time is 48-72h.

[0075] Examples 2-5 and Comparative Examples 1-8

[0076] The preparation processes of Examples 2-5 and Comparative Examples 1-7 are substantially the same as those of Example 1, except that the heat treatment methods are different, as shown in Table 1.

[0077] Table 1 Heat treatment parameters of Examples 1-5 and Comparative Examples 1-7

[0078]

[0079] Comparative Example 8

[0080] The preparation process of Comparative Example 8 is substantially the same as that of Example 1, except that Comparative Example 8 adopts a heat treatment method of solid solution treatment and one aging treatment.

[0081] The temperature of solution treatment is 1130℃, the time is 7h, and water cooling is used;

[0082] The temperature of the first aging treatment is: 720℃, the time is: 24h, and air cooling.

[0083] Performance Testing

[0084] The above-mentioned Examples 1-5 and Comparative Examples 1-8 were subjected to performance tests, mainly including room temperature stretching, 650°C high temperature stretching and 650°C endurance test. The test results are shown in Tables 2-4.

[0085] Table 2 Room temperature tensile test results

[0086]

[0087] Combining Examples 1-5 and Comparative Examples 1-8 and referring to Table 2, it can be seen that after the heat treatment method provided by the present invention, solution treatment and two-step aging treatment are adopted, and the temperature of the solution treatment is controlled to be 1100-1160°C, the holding time is 1-1.5h / 100mm, and water cooling; the temperature of the first aging step is 720-750°C, the holding time is 24-30h, and air cooling; the temperature of the second aging step is 660-700°C, the holding time is 48-72h, and air cooling. At room temperature, the tensile strength of the obtained rotor forging is above 912MPa, and the yield strength is above 483MPa.

[0088] Table 3650℃ high temperature tensile test results

[0089]

[0090]

[0091] Table 4650℃ endurance test results

[0092]

[0093]

[0094] Combining Examples 1-5 and Comparative Examples 1-8 and referring to Table 2, it can be seen that through the heat treatment method provided by the present invention, solution treatment and two-step aging treatment are adopted, and the temperature of the solution treatment is controlled to be 1100-1160°C, the holding time is 1-1.5h / 100mm, and water cooling; the temperature of the first step aging is 720-750°C, the holding time is 24-30h, and air cooling; the temperature of the second step aging is 660-700°C, the holding time is 48-72h, and air cooling. The obtained rotor forging has higher performance at high temperature. At 650°C, the tensile strength is above 786MPa, and the yield strength is above 408MPa. At 650°C and 450MPa, the lasting life is above 426h, and 650°C / 10 5 h Extrapolated endurance strength ≥240MPa.

[0095] From Comparative Example 1, it can be seen that when the solution temperature is low, the primary carbide is not completely dissolved, and the alloy has a high short-term strength, but it is not conducive to the endurance performance, especially at 650℃, 10 5 h extrapolated endurance strength is poor; it can be seen from comparative example 2 that with the increase of solid solution temperature, the grain size is excessively coarsened and the strength of the alloy is reduced; in comparative example 3, the first step aging treatment is higher than 750°C, and the formation of lamellar precipitation leads to a significant decrease in mechanical properties; in comparative example 4, the aging temperature is relatively low, the precipitation of γ′ phase is incomplete, and the strength of the alloy is low; in comparative example 5, a two-step aging heat treatment method of low temperature followed by high temperature is adopted, and the mechanical properties are relatively low; in comparative examples 6 and 7, when the second step aging temperature is 710°C, the increase in the amount of γ′ phase equilibrium precipitation is less than that in the first step aging temperature, the increment of γ′ phase precipitation in the second step is less, and the increase in strength is less; when the second step aging temperature is 650°C, the increment of γ′ phase equilibrium precipitation is larger, but the aging temperature is low, and the precipitation of γ′ phase is slow. Even if the heat preservation is 72h, the rotor index requirements cannot be met.

[0096] Reference Figure 1-3 ,from Figure 1 It can be seen that a large amount of M is precipitated at the grain boundary. 23 C6 type carbide, combined with chemical phase analysis, it can be seen that M in Example 4 23 The mass fraction of C6 carbide is 1.09%, which is beneficial for pinning grain boundaries and increasing alloy strength. Figure 2 It can be seen that a large number of spherical γ′ phases are distributed in the crystal. Combined with chemical phase analysis, it can be seen that the mass fraction of the γ′ phase in Example 4 is 6.22%, the size is small, and no other phases such as σ phase are found. Figure 3It can be seen that the size of the γ′ phase is mainly distributed in the particle size range of 10-18 nm. This part of the precipitated phase is mainly formed rapidly during the first step of aging. There is also a peak in the particle size range of 1-5 nm, and its precipitation amount is greater than the particle size range of 5-10 nm. This part of the precipitated phase is formed during the second step of aging.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A heat treatment method for a 650°C ultra-supercritical steam turbine nickel-based rotor forging, characterized in that: The heat treatment method is solution treatment and two-step aging treatment. The temperature of the solution treatment is 1100-1160°C, the holding time is 1-1.5h / 100mm, and the solution is water-cooled; The first step of aging is at a temperature of 720-750°C, with a holding time of 24-30 hours and air cooling; The second step of aging is at a temperature of 660-700°C, with a holding time of 48-72 hours and air cooling.

2. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1, characterized in that: The temperature of the solution treatment is 1140-1160°C, and the holding time is 1-1.5h / 100mm; The first step of aging is at a temperature of 735-750°C and the holding time is 24-30 hours; The second step aging temperature is 675-700℃, and the holding time is 48-72h.

3. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1 or 2, characterized in that: During solution treatment, the temperature is raised to 650-700°C according to the maximum power of the heat treatment furnace, and the temperature is evenly heated at a speed of 1.0-1.5 mm / min; then the temperature is raised to 1000-1050°C at a heating rate of 30-40°C / h, and kept warm for 2-3 hours; finally, the temperature is raised to 1100-1160°C at a heating rate of 15-20°C / h, and kept warm for 6-9 hours before being taken out of the furnace and water-cooled.

4. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1 or 2, characterized in that: The heating rates of the first aging step and the second aging step are ≤60°C / h.

5. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1 or 2, characterized in that: The chemical composition of the rotor forging includes, by mass percentage, C: 0.05-0.08%, Cr: 21.0-23.0%, Co: 6.5-8.8%, Mo: 6.0-8.8%, Al: 0.70-1.40%, Ti: 0.40-0.80%, Nb: 0.15-0.55%, B: 0.002-0.005%, Zr: 0.015-0.06%, and the balance is nickel and unavoidable impurity elements.

6. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1 or 2, characterized in that: The precipitated phase includes M 23 C6 type carbide and γ′ phase.

7. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 6, characterized in that: The mass fraction of the γ′ phase is 6-8%, M 23 The mass fraction of C6 carbide is above 1%.

8. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1, characterized in that: The room temperature yield strength of the rotor forging is ≥480MPa, the high temperature yield strength at 650℃ is ≥320MPa, and the 5 h Extrapolated endurance strength ≥240MPa.

9. The heat treatment method for 650°C ultra-supercritical steam turbine nickel-based rotor forgings according to claim 1, characterized in that: The cross-sectional size of the rotor forging is 900-1100 mm.

10. A 650°C ultra-supercritical steam turbine nickel-based rotor forging, characterized in that: Prepared by the heat treatment method according to any one of claims 1 to 9.

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