Forging process for improving grain size of gh4145 superalloy

Abstract

The present application relates to the field of high-temperature alloy forging technology, in particular to a kind of forging process for improving the grain size of GH4145 high-temperature alloy, comprising the following steps: S1, free forging: after heating and holding end, in turn, blank is upset, punching, expansion hole, round, flat end face;S2, after heating and holding end, blank is ring rolling;S3, heat treatment;The present application adopts stepped heating before starting free forging, reduces the holding time of forgings at high temperature, reduces the generation and growth of oversized grains, and at the same time reduces the process steps of high-temperature alloy before forging, and then controls the heating temperature, deformation and forging fire times in stages to realize ring forming with grain size≥6 level, tensile strength≥1268MPa, reduction of area≥44, reduce energy consumption, reduce resource waste;Ring rolling is completed in two fires, which improves the production efficiency of forgings and reduces the production cost.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy technology, specifically to a forging process for improving the grain size of GH4145 high-temperature alloy. Background Technology

[0002] GH4145 is a nickel-based superalloy strengthened by age-hardening with the γ′[Ni3(Al, Ti, Nb)] phase. It exhibits good corrosion resistance and oxidation resistance below 980℃, high strength below 800℃, and good relaxation resistance at 540℃. It is suitable for corrosion-resistant ring parts, structural parts, and bolts in aero-engines that operate below 800℃ and require high strength.

[0003] GH4145 material has a complex composition and is typically forged at high temperatures. However, forging can cause grain coarsening due to grain growth, leading to a degradation of the microstructure and properties of the high-temperature alloy.

[0004] To address the aforementioned problems, this invention proposes a rational forging process. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a forging process for improving the grain size of GH4145 high-temperature alloy.

[0006] A forging process for improving the grain size of GH4145 high-temperature alloy includes the following steps:

[0007] S1, Free Forging:

[0008] The billet is first heated to 840-860℃ in the furnace and held at that temperature, then heated to 1090-1110℃ in the furnace and held at that temperature.

[0009] After the heat preservation is completed, the billet is subjected to one-time free forging. The free forging steps include upsetting, punching, bulging, rounding, and flattening the end face to obtain the forging.

[0010] S2, Ring Rolling:

[0011] The forging obtained in step S1 is heated to 1050-1070℃ in the furnace and held at that temperature.

[0012] After the heat preservation is completed, the forging is subjected to a single ring rolling, and the total deformation of the ring rolling is 38.5% to 39.5%, to obtain a ring.

[0013] S3, Heat Treatment:

[0014] First, the ring obtained in step S2 is subjected to step solution treatment, and then step precipitation hardening is performed to obtain the forged GH4145 high-temperature alloy.

[0015] Furthermore, in steps S1 and S2, the shortest heat preservation time is calculated as 0.7 to 0.9 min / mm, and the longest heat preservation time is equal to the shortest heat preservation time plus 40 min, where mm in min / mm refers to the maximum of the two data: the diameter and the length of the billet or forging.

[0016] Note: The heat preservation regulations during furnace heating ensure that the billet is heated fully and evenly. For larger billets, the heat preservation time is calculated based on the greater of the billet diameter and length. This ensures that the entire billet reaches a uniform temperature before forging or rolling, avoiding problems such as uneven deformation and inconsistent structural stress caused by uneven temperature, and thus improving the stability of product quality and performance.

[0017] Furthermore, in steps S1 and S2, during the free forging or ring rolling process, when the temperature of the billet or forging is lower than the holding temperature, the billet or forging is returned to the furnace to be heated to the holding temperature and held again. The shortest holding time for the second holding is calculated as 0.4 to 0.6 min / mm, and the longest holding time is equal to the shortest holding time + 40 min. Here, mm in min / mm refers to the maximum of the two data: the diameter and the length of the billet or forging.

[0018] Note: The heat preservation specifications for reheating ensure that the billet is heated fully and evenly. For larger billets, the heat preservation time is calculated based on the greater of the billet diameter and length. This ensures that the entire billet reaches a uniform temperature before forging or rolling, avoiding problems such as uneven deformation and inconsistent structural stress caused by uneven temperature, and thus improving the stability of product quality and performance.

[0019] Furthermore, in steps S1 and S2, after the heat preservation is completed, the surface of the billet and forging is wrapped with heat preservation cotton with a thickness of 4.5 to 5.5 mm until the next step is carried out.

[0020] Note: Thermal insulation cotton has excellent heat insulation properties, which can effectively reduce heat loss and keep the billet at a high temperature during the transfer process. This prevents new stress concentration and cracks caused by excessive cooling, and ensures the microstructure and mechanical properties of the billet. Thermal insulation cotton can also isolate air, reduce the contact between the billet and oxygen, thereby reducing the degree of oxidation and improving the surface quality of the forging.

[0021] Further, in step S1, the initial ratio A of the outer diameter to the inner diameter of the forging is 2 to 2.2, and the diameter ratio r of the drive roller and the mandrel is 1.5 to 2. During the ring rolling process in step S2, the rotational speed of the drive roller and the feed speed of the mandrel are adjusted according to the ratio m of the outer diameter to the inner diameter of the ring to the initial ratio A, i.e., m = a / A. The adjustment method is as follows:

[0022] When m < m1, the rotational speed V1 of the driving roller is 15 - 20 r / min, and the feeding speed v1 of the core roller is 0.4 - 0.7 m / s;

[0023] When m1 < m < m2, the rotational speed V2 of the driving roller is a × m × V1, and the feeding speed v2 of the core roller is a × m × v1 / r;

[0024] When m > m2, the rotational speed V3 of the driving roller is 1.2 - 1.5 × m × V2, and the feeding speed v3 of the core roller is 1.2 - 1.5 × m × v2 / r;

[0025] Among them, m1 = 30 - 40%, m2 = 50 - 55%.

[0026] Note: During the ring rolling process, as rolling progresses, the outer diameter and inner diameter of the ring blank will gradually change. In the initial stage of ring blank rolling, relatively low rotational speeds of the driving roller and feeding speeds of the core roller are adopted, which can enable the ring blank to gradually and smoothly enter the rolling state, avoiding defects such as cracks in the blank caused by too fast deformation speed. As rolling progresses, when reaching a certain range, gradually increasing the rotational speed of the driving roller and the feeding speed of the core roller can accelerate the deformation speed of the ring, improve the rolling efficiency, shorten the production cycle of a single ring, thereby improving the production efficiency on the premise of ensuring product quality. Reasonable adjustment of the rotational speed of the driving roller and the feeding speed of the core roller can make the deformation of the ring more uniform during the rolling process, and the metal streamline more smooth, thus reducing the generation of internal stress concentration and microstructural defects, which helps to improve the mechanical properties of the ring, such as increasing strength, toughness, and fatigue life, etc.

[0027] Furthermore, in step S3, the stepped solution treatment is as follows: The blank is first held at 880 - 890 °C for 1.5 - 2.5 h, then heated in the furnace to 980 - 985 °C, held for 75 - 85 min and then water-cooled.

[0028] Note: The stepped solution treatment can improve the strength and hardness of the material and maintain its good plasticity and toughness.

[0029] Furthermore, in step S3, the stepped precipitation hardening is as follows: The blank is first held at 730 - 735 °C for 7.5 - 8.5 h, then cooled in the furnace to 620 - 625 °C, held for 7.5 - 8.5 h and then air-cooled.

[0030] Note: The stepped precipitation hardening can also improve the corrosion resistance and high-temperature stability of the alloy material.

[0031] Furthermore, during the period of furnace cooling from 730 to 735°C to 620 to 625°C, the ring is subjected to a first stage of water mist mixed cooling, and the billet is simultaneously subjected to electric pulse assisted treatment with a current of 150 to 250A and a frequency of 60 to 80Hz. During the period of furnace cooling from 620 to 625°C to room temperature, the ring is subjected to a second stage of water mist mixed cooling with a current adjusted to 300 to 400A and a frequency adjusted to 90 to 120Hz.

[0032] Explanation: Cooling the ring component with the assistance of electric pulse and water mist promotes a more uniform distribution and diffusion of metal atoms during the cooling process, inhibits grain growth, thereby refining the grain structure and improving the strength and toughness of the material. Water mist mixed cooling can enable the precipitated phase to nucleate and grow uniformly in a wider area during rapid and uniform cooling, further improving the comprehensive mechanical properties of the material.

[0033] Furthermore, the cooling medium for the first-stage water mist mixing cooling is a mixture of compressed air at 15-18 kPa and water at a flow rate of 24-26 L / h, sprayed as a water mist mixture, with a temperature of 50-60°C; the cooling medium for the second-stage water mist mixing cooling is a mixture of compressed air at 10-12 kPa and water at a flow rate of 28-30 L / h, sprayed as a water mist mixture, with a temperature of 15-25°C.

[0034] Explanation: Water mist cooling achieves uniform heat exchange by ensuring that atomized water particles fully contact the material surface, thus avoiding localized overheating or overcooling and reducing thermal stress concentration within the material.

[0035] Compared with existing high-temperature alloy forging processes, the advantages of this invention are:

[0036] (1) Before the free forging of GH4145 high-temperature alloy, the present invention adopts a stepped heating method, and the temperature is selected as the phase precipitation temperature of 850℃, which can achieve the purpose of uniform grains, reduce the storage time of the forging at high temperature, reduce the generation and growth of excessive grains, and reduce the process steps of high-temperature alloy before forging. By controlling the stage heating temperature, deformation amount and forging times, the grain size of the ring is ≥6, the tensile strength is ≥1268MPa, and the reduction of area is ≥44, so that the ring can be formed within two forging times, reducing energy consumption, reducing resource waste, improving forging production efficiency and reducing production costs.

[0037] (2) In the initial stage of ring rolling, the present invention uses a relatively low drive roller speed and mandrel feed speed, which allows the ring blank to gradually and smoothly enter the rolling state, avoiding defects such as cracks caused by excessively fast deformation speed. As rolling progresses, once a certain range is reached, the drive roller speed and mandrel feed speed are gradually increased, which can accelerate the deformation speed of the ring, improve rolling efficiency, and shorten the production cycle of a single ring. Thus, production efficiency is improved while ensuring product quality. Reasonable adjustment of drive roller speed and mandrel feed speed can make the deformation of the ring more uniform and the metal flow line smoother during the rolling process, thereby reducing the generation of internal stress concentration and microstructure defects. This helps to improve the mechanical properties of the ring, such as increasing strength, toughness and fatigue life.

[0038] (3) In the cooling process of step precipitation hardening, the present invention uses electric pulse and water mist to assist in cooling the ring, which promotes the more uniform distribution and diffusion of metal atoms during the cooling process, inhibits grain growth, thereby refines the grain structure and improves the strength and toughness of the material. The water mist mixed cooling can enable the precipitated phase to nucleate and grow uniformly in a wider area during rapid and uniform cooling, further improving the comprehensive mechanical properties of the ring. Attached Figure Description

[0039] Figure 1 This is a metallographic image of the GH4145 high-temperature alloy of Embodiment 1 of the present invention under a 100X optical microscope. Detailed Implementation

[0040] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0041] Example 1: A forging process for improving the grain size of GH4145 high-temperature alloy, comprising the following steps:

[0042] S1, Free Forging:

[0043] The billet with diameter Ф130×212mm is first heated to 850℃ in the furnace and held at that temperature, and then heated to 1100℃ in the furnace and held at that temperature.

[0044] After the heat preservation is completed, the billet is subjected to one-time free forging. The free forging steps include upsetting, punching, expanding, rolling, and flattening the end face in sequence to obtain a forging with a diameter of Ф287×Ф130×49mm.

[0045] S2, Ring Rolling:

[0046] The forging obtained in step S1 is heated to 1060°C in the furnace and held at that temperature.

[0047] After the heat preservation is completed, the forging is subjected to a single ring rolling, and the total deformation of the ring rolling is 38.9%, resulting in a ring with a diameter of Φ388×Φ292×49mm.

[0048] In steps S1 and S2, after the heat preservation is completed, the surface of the billet and forging is wrapped with heat preservation cotton with a thickness of 5mm until the next step is carried out.

[0049] S3, Heat Treatment:

[0050] First, the ring obtained in step S2 is subjected to step solution treatment, and then step precipitation hardening is performed to obtain the forged GH4145 high temperature alloy.

[0051] The stepped solution treatment is as follows: the billet is first held at 885℃ for 2 hours, then heated to 982℃ in the furnace, held for 80 minutes, and then water-cooled; the stepped precipitation hardening is as follows: the billet is first held at 72℃ for 8 hours, then cooled to 623℃ in the furnace, held for 8 hours, and then air-cooled.

[0052] In steps S1 and S2, the minimum holding time is calculated at 0.8 min / mm, and the maximum holding time is equal to the minimum holding time plus 40 min. Here, mm in min / mm refers to the greater of the diameter and length of the billet or forging; that is, the holding time in step S1 is...

[0053] In steps S1 and S2, during free forging or ring rolling, when the temperature of the billet or forging is lower than the holding temperature, the billet or forging is returned to the furnace to be heated to the holding temperature and held again. The shortest holding time for the second holding is calculated as 0.5 min / mm, and the longest holding time is equal to the shortest holding time + 40 min. Here, mm in min / mm refers to the maximum of the two data: the diameter and the length of the billet or forging.

[0054] Example 2: The difference between this example and Example 1 is that the billet is first heated to 840°C in the furnace and held at that temperature, and then heated to 1110°C in the furnace and held at that temperature.

[0055] Example 3: The difference between this example and Example 1 is that the billet is first heated to 860°C in the furnace and held at that temperature, and then heated to 1090°C in the furnace and held at that temperature.

[0056] Example 4: The difference between this example and Example 1 is that the deformation amount of free forging and the total deformation amount of ring rolling are 38.5%.

[0057] Example 5: The difference between this example and Example 1 is that the deformation amount of free forging and the total deformation amount of ring rolling are 39.5%.

[0058] Example 6: The difference between this example and Example 1 is that the forging obtained in step S1 is heated in the furnace to 1050 °C and held for heat preservation.

[0059] Example 7: The difference between this example and Example 1 is that the forging obtained in step S1 is heated in the furnace to 1070 °C and held for heat preservation.

[0060] Example 8: The difference between this example and Example 1 is that in steps S1 and S2, the shortest heat preservation time for heat preservation is calculated at 0.7 min / mm, and the shortest heat preservation time for re-heat preservation is calculated at 0.4 min / mm.

[0061] Example 9: The difference between this example and Example 1 is that in steps S1 and S2, the shortest heat preservation time for heat preservation is calculated at 0.9 min / mm, and the shortest heat preservation time for re-heat preservation is calculated at 0.6 min / mm.

[0062] Example 10: The difference between this example and Example 1 is that the stepped solution treatment is as follows: the blank is first held at 880 °C for 1.5 h, then heated in the furnace to 985 °C, held for 85 min and then water-cooled.

[0063] Example 11: The difference between this example and Example 1 is that the stepped solution treatment is as follows: the blank is first held at 890 °C for 2.5 h, then heated in the furnace to 980 °C, held for 75 min and then water-cooled.

[0064] Example 12: The difference between this example and Example 1 is that the stepped precipitation hardening is as follows: the blank is first held at 730 °C for 7.5 h, then cooled in the furnace to 625 °C, held for 8.5 h and then air-cooled.

[0065] Example 13: The difference between this example and Example 1 is that the stepped precipitation hardening is as follows: the blank is first held at 735 °C for 8.5 h, then cooled in the furnace to 620 °C, held for 7.5 h and then air-cooled.

[0066] Example 14: The difference between this example and Example 1 is that the initial ratio A of the outer diameter and inner diameter of the forging obtained in step S1 is 2.1, and the diameter ratio r of the driving roll and the core roll is 1.8. During the ring rolling process in step S2, according to the ratio m of the outer diameter and inner diameter ratio a of the ring part to the initial ratio A, that is, m = a / A, the driving roll speed and the core roll feed speed are adjusted. The adjustment method is as follows:

[0067] When m < m1, the driving roll speed V1 is 18 r / min and the core roll feed speed v1 is 0.6 m / s;

[0068] When m1 < m < m2, the rotational speed V2 of the driving roller is a × m × V1, and the feeding speed v2 of the core roller is a × m × v1 / r;

[0069] When m > m2, the rotational speed V3 of the driving roller is 1.4 × m × V2, and the feeding speed v3 of the core roller is 1.4 × m × v2 / r;

[0070] Among them, m1 = 35% and m2 = 52%.

[0071] Example 15: The difference between this example and Example 14 is that the initial ratio A of the outer diameter to the inner diameter of the forging is 2, and the diameter ratio r of the driving roller to the core roller is 1.5.

[0072] Example 16: The difference between this example and Example 14 is that the initial ratio A of the outer diameter to the inner diameter of the forging is 2.2, and the diameter ratio r of the driving roller to the core roller is 2.

[0073] Example 17: The difference between this example and Example 14 is that when m1 = 30%, the rotational speed V1 of the driving roller is 15 r / min, and the feeding speed v1 of the core roller is 0.4 m / s.

[0074] Example 18: The difference between this example and Example 14 is that when m1 = 40%, the rotational speed V1 of the driving roller is 20 r / min, and the feeding speed v1 of the core roller is 0.7 m / s.

[0075] Example 19: The difference between this example and Example 14 is that m1 = 30% and m2 = 55%.

[0076] Example 20: The difference between this example and Example 14 is that m1 = 40% and m2 = 50%.

[0077] Example 21: The difference between this example and Example 14 is that when m2 = 50%, the rotational speed V3 of the driving roller is 1.2 × m × V2, and the feeding speed v3 of the core roller is 1.2 × m × v2 / r.

[0078] Example 22: The difference between this example and Example 14 is that when m2 = 55%, the rotational speed V3 of the driving roller is 1.5 × m × V2, and the feeding speed v3 of the core roller is 1.5 × m × v2 / r.

[0079] Example 23: This example differs from Example 1 in that, during the furnace cooling process from 732°C to 623°C, the ring undergoes a first-stage water mist cooling process, while the billet is simultaneously subjected to electric pulse assisted treatment with a current of 200A and a frequency of 70Hz; during the furnace cooling process from 623°C to room temperature, the ring undergoes a second-stage water mist cooling process, with the current adjusted to 350A and the frequency adjusted to 105Hz; the cooling medium for the first-stage water mist cooling is a mixture of 16.5KPa compressed air and 25L / h water sprayed out as a water mist mixture, with a cooling medium temperature of 55°C; the cooling medium for the second-stage water mist cooling is a mixture of 11KPa compressed air and 29L / h water sprayed out as a water mist mixture, with a cooling medium temperature of 20°C.

[0080] Example 24: This example differs from Example 23 in that the first-stage water mist mixing cooling uses 15KPa compressed air mixed with 24L / h of water to spray a water mist mixture, and the temperature of the cooling medium is 50℃; the second-stage water mist mixing cooling uses 10KPa compressed air mixed with 28L / h of water to spray a water mist mixture, and the temperature of the cooling medium is 15℃.

[0081] Example 25: This example differs from Example 23 in that the cooling medium of the first-stage water mist mixing cooling is a mixture of 18 kPa compressed air and 26 L / h water sprayed out as a water mist mixture, and the temperature of the cooling medium is 20°C; the cooling medium of the second-stage water mist mixing cooling is a mixture of 12 kPa compressed air and 30 L / h water sprayed out as a water mist mixture, and the temperature of the cooling medium is 25°C.

[0082] Example 26: This example differs from Example 23 in that, during the period of furnace cooling from 732°C to 623°C, the ring is subjected to a first stage of water mist mixed cooling, and the billet is simultaneously subjected to electric pulse assisted treatment with a current of 150A and a frequency of 60Hz; during the period of furnace cooling from 623°C to room temperature, the ring is subjected to a second stage of water mist mixed cooling, with the current adjusted to 400A and the frequency adjusted to 120Hz.

[0083] Example 27: This example differs from Example 23 in that, during the period of furnace cooling from 732°C to 623°C, the ring is subjected to a first stage of water mist mixed cooling, and the billet is simultaneously subjected to electric pulse assisted treatment with a current of 250A and a frequency of 80Hz; during the period of furnace cooling from 623°C to room temperature, the ring is subjected to a second stage of water mist mixed cooling, with the current adjusted to 300A and the frequency adjusted to 90Hz.

[0084] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and aims to illustrate the practical application effect of the present invention.

[0085] The grain size and tensile strength of the GH4145 forged in each embodiment were tested. Each embodiment was tested three times, and the average data of the three tests was taken as the final experimental result.

[0086] 1. Investigate the effects of various parameters of free forging, ring rolling and heat treatment on the grain size and tensile strength of GH4145.

[0087] Table 1. Grain size and tensile strength of Examples 1-13 and Comparative Examples 1-3

[0088]

[0089] The difference between Comparative Example 1 and Example 1 is that in step S1, the billet is directly heated to 1100°C without a step heating to 850°C.

[0090] The difference between Comparative Example 2 and Example 1 is that in step S3, the solution treatment is heated to 982°C in one step;

[0091] The difference between Comparative Example 3 and Example 1 is that in step S3, the precipitation hardening treatment is heated to 623°C in one step;

[0092] As shown in Table 1, the grain size and tensile strength of GH4145 in Comparative Example 1 (lacking step heating before forging), Comparative Example 2 (lacking step heating for solution treatment), and Comparative Example 3 (lacking step heating for precipitation hardening treatment) were significantly lower than those in Examples 1-13. Therefore, the step treatment played a certain role in improving the grain size and tensile strength of GH4145.

[0093] Comparing Examples 1-13, it can be seen that excessively small or large parameter differences in stepped heating, excessively small or large deformation amounts in free forging and ring rolling, excessively small or large furnace heating temperatures before ring rolling, excessively small or large calculations of the minimum holding time, excessively small or large temperature differences in stepped solution treatment, and excessively small or large temperature differences in stepped precipitation hardening treatment will all reduce the grain size or tensile strength of GH4145. Therefore, in summary, the parameter effect of Example 1 is relatively better, and as... Figure 1 As shown, the grain distribution in Example 1 is uniform and the grain size is high.

[0094] 2. Investigate the effects of parameters that adjust the drive roll speed and core roll feed speed based on the ratio of the outer diameter to the inner diameter of the ring roll on the grain size and tensile strength of GH4145.

[0095] Table 2 Grain size and tensile strength of Examples 14-22

[0096]

[0097]

[0098] As shown in Table 2, adjusting the drive roll speed and core roll feed speed according to the ratio of the outer diameter to the inner diameter of the ring roll significantly improved the average grain size and tensile strength compared to Examples 1-13. Therefore, the adjustment method significantly enhanced the performance of GH4145.

[0099] Furthermore, comparing Examples 14 to 22, it can be seen that if the initial ratio and diameter ratio are too small or too large, or if m and the corresponding drive roller speed are too small or too large, the grain size and tensile strength of GH4145 will be reduced. Therefore, in summary, the parameter effect of Example 14 is relatively better.

[0100] 3. Investigate the effects of parameters for assisted cooling by a mixture of electrical pulses and water mist during stepped precipitation hardening on the grain size and tensile strength of GH4145.

[0101] Table 3 Grain size and tensile strength of Examples 23-27 and Comparative Examples 4-5

[0102]

[0103] The difference between Comparative Example 4 and Example 23 is that the parameters of the electrical pulse remain unchanged;

[0104] The difference between Comparative Example 5 and Example 23 is that the cooling parameters remain unchanged when the two water mists are mixed;

[0105] As shown in Table 3, Example 23 further improved the average grain size and tensile strength compared to Example 14. Compared to Examples 23-27, the tensile strength of Comparative Example 4, which lacked the two-stage variation of electric pulse, and Comparative Example 5, which lacked the two-stage variation of water mist mixed cooling, was reduced. Therefore, the parameter changes of electric pulse and water mist mixed cooling according to the cooling temperature have a certain effect on improving the grain size and tensile strength of GH4145.

[0106] Comparing Examples 23-27, it can be seen that if the parameters of the two electrical pulse assisted processing are too small or too large, and the parameters of the two water mist mixed cooling processes are too small or too large, the grain size and tensile strength of GH4145 will be reduced. Therefore, in summary, the parameter effect of Example 27 is relatively better.

[0107] As can be seen from the above investigations 1 to 3, the grain size of GH4145 forged by the present invention is ≥6 and the tensile strength is ≥1268MPa.

Claims

1. A forging process for improving the grain size of GH4145 high-temperature alloy, characterized in that, It includes the following steps: S1. Open-die forging: The blank is first heated in the furnace to 840 - 860 °C and held, then heated in the furnace to 1090 - 1110 °C and held; After the holding is completed, the blank is subjected to one-pass open-die forging. The total deformation amount of the open-die forging is 68.4%. The steps of the open-die forging sequentially include upsetting, punching, expanding the hole, rolling into a circle, and flattening the end face to obtain a forging; S2. Ring rolling: The forging obtained in step S1 is heated in the furnace to 1050 - 1070 °C and held; After the holding is completed, the forging is subjected to one-pass ring rolling. The total deformation amount of the ring rolling is 38.5 - 39.5% to obtain a ring; The initial ratio A of the outer diameter to the inner diameter of the forging obtained in step S1 is 2 - 2.2, and the diameter ratio r of the driving roll to the core roll is 1.5 - 2. During the ring rolling process in step S2, according to the ratio m of the outer diameter to the inner diameter ratio a of the ring to the initial ratio A, that is, m = a / A, the rotational speed of the driving roll and the feeding speed of the core roll are adjusted. The adjustment method is as follows: When m < m1, the rotational speed V1 of the driving roll is 15 - 20 r / min, and the feeding speed v1 of the core roll is 0.4 - 0.7 m / s; When m1 < m < m2, the rotational speed V2 of the driving roll is a × m × V1, and the feeding speed v2 of the core roll is a × m × v1 / r; When m > m2, the rotational speed V3 of the driving roll is 1.2 - 1.5 × m × V2, and the feeding speed v3 of the core roll is 1.2 - 1.5 × m × v2 / r; Where, m1 = 30 - 40%, m2 = 50 - 55%; S3. Heat treatment: First, the ring obtained in step S2 is subjected to stepped solution treatment, and then stepped precipitation hardening is carried out. The stepped precipitation hardening is as follows: The blank is first held at 730 - 735 °C for 7.5 - 8.5 h, then cooled in the furnace to 620 - 625 °C, held for 7.5 - 8.5 h and then air-cooled to room temperature. During the period of cooling in the furnace from 730 - 735 °C to 620 - 625 °C, the ring is subjected to a first-stage water mist mixed cooling, and at the same time, the blank is subjected to electro-pulse assisted treatment with a current of 150 - 250 A and a frequency of 60 - 80 Hz; during the period of cooling in the furnace from 620 - 625 °C to room temperature, the ring is subjected to a second-stage water mist mixed cooling, the current is adjusted to 300 - 400 A, and the frequency is adjusted to 90 - 120 Hz to obtain the forged GH4145 superalloy.

2. The forging process for improving the grain size of GH4145 high-temperature alloy as described in claim 1, characterized in that, In steps S1 and S2, the shortest holding time for the holding is calculated according to 0.7 - 0.9 min / mm, and the longest holding time = the shortest holding time + 40 min, where mm in min / mm refers to the maximum value of the two data of the diameter and length of the blank or forging.

3. The forging process for improving the grain size of GH4145 high-temperature alloy as described in claim 1, characterized in that, In steps S1 and S2, during the open-die forging or ring rolling process, when the temperature of the blank or forging is lower than the holding temperature, the blank or forging is returned to the furnace and heated to the holding temperature and held again. The shortest holding time for the re-holding is calculated according to 0.4 - 0.6 min / mm, and the longest holding time = the shortest holding time + 40 min, where mm in min / mm refers to the maximum value of the two data of the diameter and length of the blank or forging.

4. The forging process for improving the grain size of GH4145 high-temperature alloy as described in claim 1, characterized in that, In steps S1 and S2, after the heat preservation is completed, the surface of the billet and forging is wrapped with heat preservation cotton with a thickness of 4.5~5.5mm until the next step is carried out.

5. The forging process for improving the grain size of GH4145 high-temperature alloy as described in claim 1, characterized in that, In step S3, the stepped solution treatment is as follows: the billet is first kept at 880~890℃ for 1.5~2.5h, then heated to 980~985℃ in the furnace, kept at 75~85min, and then water cooled.

6. The forging process for improving the grain size of GH4145 high-temperature alloy as described in claim 1, characterized in that, The cooling medium for the first-stage water mist mixing cooling is a mixture of compressed air at 15~18KPa and water at a flow rate of 24~26L / h, sprayed as a water mist mixture, with a temperature of 50~60℃. The cooling medium for the second-stage water mist mixing cooling is a mixture of compressed air at 10~12KPa and water at a flow rate of 28~30L / h, sprayed as a water mist mixture, with a temperature of 15~25℃.

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