A notch-insensitive GH4141 high-temperature alloy forged bar and a preparation method thereof

Abstract

This invention relates to the field of high-temperature alloy technology, specifically to a notch-free GH4141 high-temperature alloy forging bar and its preparation method. In the microstructure of this GH4141 high-temperature alloy forging bar, M6C carbides are distributed in spherical granular form at the grain boundaries; the forging bar exhibits a high-temperature notch creep rupture time ≥40h under 732℃ temperature and 603MPa stress conditions, and the fracture locations are all located in the smooth segment.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy technology, specifically to a notch-free, non-sensitive GH4141 high-temperature alloy forging bar and its preparation method. Background Technology

[0002] GH4141 high-temperature alloy is a precipitation-hardening nickel-based wrought alloy, with γ′ phase and M6C carbide as its main strengthening phases. Due to its excellent high-temperature strength (suitable for temperatures below 870℃) and good oxidation resistance (suitable for temperatures below 980℃), this alloy is widely used in the manufacture of key hot-end load-bearing components for aerospace engines.

[0003] However, the GH4141 alloy has a high degree of alloying, making it prone to severe elemental segregation during solidification, accompanied by the precipitation of a large number of coarse carbides between dendrites. These as-cast carbides mainly include MC, M6C, and M... 23 Types such as C6 typically exhibit strip-like, block-like, or Chinese character-shaped distributions, and are relatively large in size. Conventional homogenization heat treatments are unlikely to completely dissolve or eliminate them. Studies have shown that the distribution, quantity, and size of carbides have a decisive influence on the hot working plasticity and final mechanical properties of alloys: large-sized MC and M6C carbides in the as-cast microstructure significantly reduce the hot working plasticity of the alloy and increase the difficulty of billet preparation; while M6C and M... 23 The precipitation behavior of C6 carbides at the grain boundaries of the forged bar is directly related to the high-temperature creep performance of the material.

[0004] Current research mainly focuses on improving the hot workability, carbide distribution uniformity, and grain size control of GH4141 alloy. For example, invention patent CN114472770B discloses a forging process for large round bars of GH141 alloy, employing a combination of fast forging and precision forging. By strictly controlling the heating process and deformation amount, it successfully obtained forged bars with relatively uniform grain size. However, this patent does not address the carbide distribution characteristics of the forged bar and their impact on creep rupture performance. Similarly, patent application CN116809829A discloses a forging method to improve the carbide banding distribution of GH4141 alloy. By introducing a multi-heat upsetting process during the initial forging, it effectively improves the carbide banding distribution. However, this patent also does not delve into the effects of the specific type, size, and precipitation location of carbides on the alloy's creep rupture performance, particularly notch sensitivity.

[0005] With the continuous improvement of aero-engine performance parameters, more stringent requirements are being placed on the high-temperature creep resistance of materials. Currently, for GH4141 alloy, not only is a high-temperature notch creep rupture time of ≥23 hours required at 732℃ / 603MPa, but the fracture location must also be located in a smooth segment, i.e., completely eliminating notch sensitivity. However, research on how to systematically eliminate the notch sensitivity of GH4141 alloy through process control has not yet been reported.

[0006] Therefore, it is necessary to provide a GH4141 high-temperature alloy forging bar that can eliminate notch sensitivity and its preparation method to meet the urgent needs of high-end equipment for material reliability and consistency. Summary of the Invention

[0007] In view of this, in order to solve the above problems, the purpose of this invention is to provide a notch-free GH4141 high-temperature alloy forging bar and its preparation method, which can at least solve the problems of low high-temperature creep performance and notch sensitivity of existing GH4141 alloys.

[0008] The first aspect of this invention proposes a notch-free GH4141 high-temperature alloy forging bar, whose chemical composition by mass percentage includes: C: 0.06-0.12%, Cr: 18.0-20.0%, Co: 10.0-12.0%, Mo: 9.50-10.50%, Al: 1.4-1.8%, Ti: 3.0-3.5%, B: 0.003-0.010%, Si≤0.5%, Mn≤0.5%, Cu≤0.5%, P≤0.015%, S≤0.015%, Fe≤5.0%, Zr≤0.07%, with the balance being Ni and unavoidable impurities; in the microstructure of the forging bar, M6C carbides are distributed in spherical granules at the grain boundaries; the high-temperature notch creep fracture time of the forging bar under 732℃ temperature and 603MPa stress conditions is ≥40h, and the fracture location is located in the smooth segment.

[0009] The second aspect of this invention provides a method for preparing a notch-free, sensitive GH4141 high-temperature alloy forging bar. The method comprises the following steps: sequentially subjecting a GH4141 high-temperature alloy ingot to a first homogenization heat treatment, pre-forging, a second homogenization heat treatment, a second forging, and subsequent forging to obtain the forging bar. The first homogenization heat treatment is performed at a temperature of 1160-1200℃ for a holding time of 36-48 hours. The second homogenization heat treatment is performed at a temperature of 1170℃-1190℃ for a holding time of 10-15 hours.

[0010] In some embodiments, after the first homogenization heat treatment and before pre-forging, a cooling process is also included: first, the ingot furnace is cooled to 950-1050°C, and then the ingot is directly transferred to the high-speed forging machine heating furnace for pre-forging heating and heat preservation, or it is air-cooled to room temperature for subsequent use.

[0011] In some embodiments, pre-forging includes: heating the ingot after the first homogenization heat treatment to 1130-1160°C, holding it at that temperature for 2-3 hours, and then performing at least three upsetting and drawing forging processes to obtain a first intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%.

[0012] In some embodiments, the secondary forging includes: cooling the intermediate billet after the second homogenization heat treatment to 1130-1160°C in a furnace, holding it at that temperature for 2-3 hours, and then performing at least four upsetting and drawing forging cycles to obtain a second intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%.

[0013] In some embodiments, the subsequent forging includes a final forging: the second intermediate billet obtained after two forgings is heated to 1100-1120°C, held for 2-3 hours, and then subjected to a single forging process with a deformation of 45%-60%, to obtain a quick-forging billet.

[0014] In some embodiments, subsequent forging also includes radial forging after the final rapid forging: heating the rapid forging billet to 1100℃-1120℃, holding it at that temperature for 2-3 hours, performing one round of radial forging, with a deformation of 30%-45%, to obtain a forged bar.

[0015] In some embodiments, the preparation method further includes the step of heat treatment of the forged bar: performing solution treatment and aging treatment in sequence; the solution treatment temperature is 1070-1100℃, and the bar is held at the temperature and then water-cooled; the aging treatment temperature is 750-770℃, and the bar is held at the temperature and then air-cooled.

[0016] In some embodiments, insulation cotton is used to wrap the billet during pre-forging, secondary forging, and subsequent drawing forging.

[0017] In some embodiments, the GH4141 high-temperature alloy ingot is prepared by a dual process of vacuum induction melting and vacuum arc remelting.

[0018] The beneficial effects of the notch-sensitive GH4141 high-temperature alloy forging bar and its preparation method provided by this invention are as follows: 1. The GH4141 forged bar prepared in this application has a uniform microstructure, and its notch creep retardation performance is significantly improved. All M6C carbides in the bar microstructure precipitate along the grain boundaries. This improves the grain boundary strength, but the large-scale precipitation of M6C also consumes carbon elements near the grain boundaries, preventing the precipitation of M6C carbides, which are detrimental to creep retardation performance, during aging. 23 The C6 content was significantly reduced. The bar stock exhibited a high-temperature notch creep rupture time of ≥40h under 732℃ temperature and 603MPa stress conditions, and the fracture locations were all in the smooth section.

[0019] 2. The notch-free sensitive GH4141 high-temperature alloy forging method proposed in this invention utilizes a forging method consisting of two homogenization processes, two rapid forging processes, and subsequent forging. This method rationally controls process parameters such as forging and homogenization heating temperature, holding time, and deformation amount, precisely controlling the type and distribution characteristics of carbide precipitation. During hot working, the size of MC carbides decreases and they become uniformly dispersed, while all M6C carbides precipitate along grain boundaries. 23 C6 carbides should be precipitated as little as possible.

[0020] 3. Two-stage homogenization is more effective at resolving carbides than single-stage homogenization. The first homogenization heat treatment can resolve all γ′ phases and M... 23 C6 and some small-sized M6C carbides dissolve back into the matrix, improving the alloy's hot working plasticity and providing the necessary microstructure for the first forging deformation. However, large-sized M6C carbides cannot be completely dissolved, especially large ingots, which require higher temperatures and longer times to fully dissolve. The second homogenization heat treatment is performed on the intermediate billet after upsetting and drawing. The upsetting and drawing process accumulates a certain amount of stored energy in the forged bar microstructure, providing sufficient driving force for carbide dissolution. During the second homogenization heat treatment, large-sized M6C carbides can be completely dissolved in a short time, and MC carbides are partially dissolved, making the alloy microstructure more homogeneous. Furthermore, the total time for the two homogenization processes is shorter than that for the single homogenization process, improving production efficiency. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0022] Figure 1 The microstructure of the GH4141 alloy bar after heat treatment in Example 1 of this invention; Figure 2The microstructure of the GH4141 alloy bar after heat treatment in Example 2 of this invention; Figure 3 This is the microstructure of the GH4141 alloy bar after heat treatment in Comparative Example 1 of the present invention; Figure 4 This is the microstructure of the GH4141 alloy bar after heat treatment in Comparative Example 2 of the present invention; Figure 5 This is the microstructure of the GH4141 alloy bar after heat treatment in Comparative Example 3 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0024] The first aspect of this invention proposes a notch-free GH4141 high-temperature alloy forging bar, whose chemical composition, by mass percentage, includes: C: 0.06–0.12%, Cr: 18.0–20.0%, Co: 10.0–12.0%, Mo: 9.50–10.50%, Al: 1.4–1.8%, Ti: 3.0–3.5%, B: 0.003–0.010%, Si≤0.5%, Mn≤0.5%, Cu≤0.5%, P≤0.015%, S≤0.015%, Fe≤5.0%, Zr≤0.07%, with the balance being Ni and unavoidable impurities. The microstructure of the forging bar is uniform, and the notch creep performance of the bar is significantly improved. Specifically, in the bar microstructure, all M6C carbides precipitate along the grain boundaries. On the one hand, this increases the grain boundary strength; on the other hand, the large-scale precipitation of M6C consumes carbon elements near the grain boundaries, leading to the precipitation of M6C carbides during aging, which is detrimental to creep aging performance. 23 The C6 content was significantly reduced. The bar stock exhibited a high-temperature notch creep rupture time of ≥40h under 732℃ temperature and 603MPa stress conditions, and the fracture locations were all in the smooth section.

[0025] The second aspect of this invention provides a method for preparing a notch-free, sensitive GH4141 high-temperature alloy forging bar. The method comprises the following steps: sequentially subjecting a GH4141 high-temperature alloy ingot to a first homogenization heat treatment, pre-forging, a second homogenization heat treatment, a second forging, and subsequent forging to obtain the forging bar. The first homogenization heat treatment is performed at a temperature of 1160-1200℃ for a holding time of 36-48 hours. The second homogenization heat treatment is performed at a temperature of 1170℃-1190℃ for a holding time of 10-15 hours.

[0026] The notch-free sensitive GH4141 high-temperature alloy forging method proposed in this invention employs a forging process involving two homogenization processes, two rapid forging processes, and subsequent forging. This method rationally controls process parameters such as forging and homogenization heating temperatures, holding times, and deformation amounts, precisely controlling the types and distribution characteristics of carbide precipitation. During hot working, this results in reduced MC carbide size and uniform dispersion, with all M6C carbides precipitating along grain boundaries. 23 To minimize the precipitation of C6 carbides, a first homogenization heat treatment is performed at 1160-1200℃ for 36-48 hours. The aim is to eliminate elemental segregation and simultaneously promote the precipitation of the γ′ phase and M phase. 23 C6 and some small-sized M6C carbides dissolve back into the matrix, improving the alloy's hot workability. Subsequent pre-forging not only breaks down the coarse, cast columnar crystals but also refines the grains through dynamic recrystallization and welds in the internal porosity. A second homogenization heat treatment at 1170-1190℃ for 10-15 hours follows. During this process, large-sized M6C carbides can dissolve completely back into the matrix in a short time. Although the dissolution temperature of MC carbides is higher than the alloy's initial melting point and cannot be completely dissolved, some of the broken small-sized MC carbides can still dissolve, further promoting the dissolution of residual point segregation after pre-forging. This also controls grain size, preventing mixed crystal formation. Furthermore, the combined time of the two homogenization processes is shorter than that of a single homogenization process, improving production efficiency. Finally, through multi-directional, large-deformation processing involving secondary forging and subsequent forging (including radial forging), the network distribution of carbides and brittle phases is completely broken up, the grains are sufficiently refined, and a microstructure conducive to uniform stress distribution is formed. This method, through the organic combination of multiple thermal cycles and deformation, ultimately eliminates the notch sensitivity of the alloy during service, significantly improving the material's strength, plasticity, and thermal stability, ensuring reliable and consistent mechanical properties of the forged bar under high-temperature and complex stress.

[0027] In some embodiments, after the first homogenization heat treatment and before pre-forging, a cooling process is also included: the ingot is first cooled to 950-1050°C (e.g., 1000°C) in the furnace, and then directly transferred to the high-speed forging mill heating furnace for pre-forging heating and heat preservation, or it is air-cooled to room temperature for subsequent use. Specifically, cooling the ingot to 950-1050°C in the furnace first can avoid thermal stress cracks caused by the ingot cooling too quickly when it is directly removed from the furnace at a high temperature. If the method of cooling the ingot in the furnace first and then directly transferring it to the high-speed forging mill heating furnace is adopted, the residual heat of the furnace itself can be used to shorten the reheating time before forging and improve energy efficiency; alternatively, the method of cooling the ingot in the furnace first and then air-cooling it to room temperature can be adopted for subsequent forging.

[0028] In some embodiments, pre-forging includes: heating the ingot after the first homogenization heat treatment to 1130-1160°C and holding it at that temperature for 2-3 hours to ensure that the alloy has sufficient thermoplasticity to withstand large deformations while avoiding excessive temperature leading to grain coarsening or localized overheating; then performing at least three upsetting and drawing forging cycles, using repeated compression and elongation deformation to break up the coarse columnar crystals and dendritic networks, forcing dynamic recrystallization of the as-cast structure to obtain a first intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%, which ensures that the deformation penetrates to the core of the billet to break up carbides and brittle phases, and effectively prevents forging cracks induced by excessive single deformation. After drawing, an octagonal cross-section intermediate billet is obtained, which has a more uniform stress distribution and temperature drop control compared to a square billet, effectively suppressing the generation of corner cracks, and providing a uniform and defect-free transition billet for the subsequent second homogenization heat treatment and final forging.

[0029] In some embodiments, the secondary forging includes: cooling the intermediate billet after the second homogenization heat treatment to 1130-1160°C in a furnace, holding it at that temperature for 2-3 hours, and then performing at least four upsetting and drawing forging cycles to obtain a second intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%. This process can further break down the remaining coarse grains and carbide networks, achieving deep homogenization of the microstructure and fine grain strengthening. Compared to pre-forging, this stage involves more forging passes. By accumulating a larger amount of plastic deformation, it can fully drive the alloy to undergo more complete dynamic recrystallization, completely eliminating any possible mixed-grain structures and further refining and unifying the grain size. At the same time, strictly controlling the upsetting (15%-35%) and elongation (20%-40%) deformation per pass ensures that the core and surface deformations are coordinated and consistent, avoiding the formation of uneven deformation zones. In addition, the multiple multi-directional forgings in this stage help to further break down and disperse the residual primary carbides and brittle phases, thereby significantly improving the alloy's strength, plasticity, and creep properties, preparing the microstructure for subsequent radial forging into high-quality, notch-free finished forged bars.

[0030] In some embodiments, subsequent forging includes a final-heat rapid forging: the second intermediate billet obtained after two forgings is heated to 1100-1120°C, held for 2-3 hours, and subjected to a single-heat elongation forging with a deformation of 45%-60%, resulting in a rapid-forging billet. This process can significantly accumulate deformation energy, inducing large-scale dynamic recrystallization in a region slightly below the grain growth zone without grain growth, thereby simultaneously refining and homogenizing the grains during deformation. This process, by precisely shaping the billet and obtaining regular cross-sectional dimensions, provides high-quality billets with regular shapes, uniform temperatures, and refined microstructures for subsequent radial forging, ensuring the stability of the radial forging process and the uniformity of the surface quality and internal structure of the finished forged bar, providing an important guarantee for eliminating notch sensitivity in the finished product.

[0031] In some embodiments, subsequent forging also includes radial forging after the final rapid forging, comprising: heating the rapid forging billet to 1100℃-1120℃, holding it at that temperature for 2-3 hours, performing one round of radial forging, with a deformation of 30%-45%, to obtain a forged bar. Through high-precision, high-frequency radial forging, a GH4141 high-temperature alloy forged bar with uniform microstructure, fine grains, no surface defects, and precise dimensions is finally obtained, fundamentally eliminating microstructural defects that lead to stress concentration and achieving the goal of no notch sensitivity.

[0032] In some embodiments, the preparation method further includes a step of heat treatment of the forged bar: sequential solution treatment and aging treatment to impart the GH4141 alloy with the excellent mechanical properties required for final service. The solution treatment temperature is 1070-1100℃, allowing the carbides and some strengthening phases precipitated during the preceding forging process to fully dissolve back into the austenitic matrix. After holding at this temperature for one hour, the bar is water-cooled to retain high concentrations of solute elements and vacancies within the supersaturated solid solution, laying the compositional foundation for subsequent aging precipitation and effectively controlling the matrix grain size to prevent abnormal grain growth. The aging treatment temperature is 760±10℃, for example, 760℃, followed by holding at this temperature for 16 hours and then air-cooling to promote the uniform precipitation of fine and dispersed γ' phase [Ni3(Al,Ti)] and carbides within the grains and at grain boundaries. These coherent precipitates effectively hinder dislocation movement, thereby producing a significant precipitation strengthening effect. After this solution and aging treatment, the forged bar not only obtains a high-strength matrix, but also optimizes the grain boundary state through the rational distribution of grain boundary precipitates, significantly improving creep resistance and endurance. Ultimately, the finished product possesses excellent room-temperature tensile properties, high-temperature strength, and microstructural thermal stability, fully meeting the stringent requirements for material performance consistency and reliability in key hot-end components. Following solution and aging treatments, microstructure and creep resistance testing can be performed. The creep test employs a combined creep test with both smooth sections and notches.

[0033] In some embodiments, during the elongation forging process involving pre-forging, secondary forging, and subsequent forging (including final forging and radial forging), insulating cotton is used to wrap the billet. By wrapping it with insulating cotton, the heat radiation and convection heat loss on the billet surface can be effectively reduced, allowing the billet to maintain a more uniform temperature field during forging transfer and deformation, significantly reducing the temperature difference between the surface and the core, thereby avoiding a surge in deformation resistance or surface cracks due to excessively low surface temperature.

[0034] In some embodiments, GH4141 high-temperature alloy ingots are prepared using a dual process of vacuum induction melting and vacuum arc remelting. Ingots prepared by this dual process have lower impurity content, fewer shrinkage cavities and porosity defects, and finer dendritic structures, providing a good microstructure foundation for subsequent homogenization heat treatment and hot working deformation, effectively reducing the risk of hot working cracking.

[0035] The present invention will be further described in detail below through specific embodiments and comparative examples.

[0036] Example 1 This invention provides a notch-free, non-sensitive GH4141 high-temperature alloy forged bar and its preparation method. The finished bar has a diameter of Φ250mm. The preparation method includes the following steps: A. Ingot Preparation: The original billet was a GH4141 high-temperature alloy ingot, which had undergone vacuum induction remelting and vacuum arc remelting. The ingot size was Φ508mm. The chemical composition of the ingot, by mass percentage, was: C: 0.08%, Cr: 19.0%, Co: 11.0%, Mo: 10.0%, Al: 1.6%, Ti: 3.2%, B: 0.006%, Si: 0.10%, Mn: 0.10%, Cu: 0.05%, P: 0.008%, S: 0.002%, Fe: 3.0%, Zr: 0.04%, with the balance being Ni and unavoidable impurities.

[0037] B, First homogenization heat treatment: The ingot is heated to 1160℃ and held for 48 hours for high-temperature homogenization treatment. After the holding period, it is furnace cooled to 1000℃ and then air-cooled to room temperature.

[0038] C. Pre-forging: The homogenized ingot is reheated to 1150℃ and held for 3 hours before pre-forging. Three heat treatments are used to perform the clamping and upsetting and drawing operations in sequence; the upsetting deformation is 25%, and the drawing deformation is 20%. During drawing, the billet is wrapped with insulating cotton; after drawing, the first intermediate billet with an octagonal cross section is obtained.

[0039] D. Second homogenization heat treatment: The first intermediate billet is heated to 1190℃ and held for 10 hours for the second homogenization treatment.

[0040] E. Secondary forging: The intermediate billet after the second homogenization treatment is cooled to 1160℃ in the furnace and held for 2 hours before secondary forging. Four heat treatments are used for upsetting and drawing forging in sequence; the upsetting deformation is 20%, and the drawing deformation is 30%. During drawing, the billet is wrapped with insulating cotton; after drawing, a second intermediate billet with an octagonal cross section is obtained.

[0041] F, final forging: The second intermediate billet is heated to 1120℃ and held for 2 hours, and then subjected to one forging pass. The forging deformation is 60%. During the forging process, insulation cotton is used to wrap the billet to obtain a quick-forging billet.

[0042] G. Radial forging: Heat the fast forging billet to 1120℃, hold for 2 hours, and perform one round of radial forging. The radial forging deformation is 45%. During radial forging, use insulating cotton to wrap the billet to obtain the finished forging bar.

[0043] H. Performance Heat Treatment: The forged bar undergoes performance heat treatment, consisting of solution treatment and aging treatment. The solution treatment process involves holding at 1080℃ for 1 hour, followed by water cooling; the aging treatment process involves holding at 760℃ for 16 hours, followed by air cooling.

[0044] The microstructure of the GH4141 high-temperature alloy forged bar prepared by the above method is as follows: Figure 1 As shown, the microstructure is uniform, with MC carbides evenly dispersed and without aggregation, while M6C carbides are all precipitated discontinuously in granular form along the grain boundaries. High-temperature notch creep rupture performance tests were conducted at 732℃ / 603MPa, and the fracture times of the bars were 42.8h and 43.4h, respectively, with both fracture locations located in the smooth section, indicating that the forged bar has no notch sensitivity.

[0045] Example 2 This invention provides a notch-free, non-sensitive GH4141 high-temperature alloy forged bar and its preparation method. The finished bar has a diameter of Φ230mm. The preparation method includes the following steps: A. Ingot Preparation: The original billet is a GH4141 high-temperature alloy ingot that has undergone vacuum induction remelting and vacuum arc remelting. The chemical composition of the ingot, by mass percentage, includes: C: 0.10%, Cr: 18.5%, Co: 10.5%, Mo: 10.50%, Al: 1.5%, Ti: 3.4%, B: 0.009%, Si: 0.15%, Mn: 0.08%, Cu: 0.03%, P: 0.006%, S: 0.001%, Fe: 4.0%, Zr: 0.02%, with the balance being Ni and unavoidable impurities.

[0046] B, First homogenization heat treatment: The ingot is heated to 1200℃ and held for 36 hours for high-temperature homogenization treatment. After the holding period, it is cooled to 1000℃ in the furnace and then directly transferred to the high-speed forging furnace for pre-forging heating and holding.

[0047] C. Pre-forging: The homogenized ingot is heated to 1160℃ and held for 3 hours before pre-forging. Three heat treatments are used to perform the clamping and upsetting and drawing operations in sequence; the upsetting deformation is 35% and the drawing deformation is 40%. During drawing, the billet is wrapped with insulating cotton; after drawing, the first intermediate billet with an octagonal cross section is obtained.

[0048] D. Second homogenization heat treatment: The first intermediate billet is heated to 1170℃ and held for 15 hours for the second homogenization treatment.

[0049] E. Secondary forging: The intermediate billet after the second homogenization treatment is cooled to 1130℃ in the furnace and held for 3 hours before secondary forging. Four heat treatments are used for upsetting and drawing forging in sequence; the upsetting deformation is 30% and the drawing deformation is 40%. During drawing, the billet is wrapped with insulating cotton; after drawing, a second intermediate billet with an octagonal cross section is obtained.

[0050] F, final forging: The second intermediate billet is heated to 1100℃ and held for 3 hours, and then subjected to one forging pass. The forging deformation is 45%. During the forging process, insulation cotton is used to wrap the billet to obtain a quick-forging billet.

[0051] G. Radial forging: Heat the fast forging billet to 1100℃, hold for 3 hours, and perform one round of radial forging. The radial forging deformation is 30%. During radial forging, use insulating cotton to wrap the billet to obtain the finished forging bar.

[0052] H. Performance Heat Treatment: The forged bar undergoes performance heat treatment, consisting of solution treatment and aging treatment. The solution treatment process involves holding at 1100℃ for 1 hour, followed by water cooling; the aging treatment process involves holding at 760℃ for 16 hours, followed by air cooling.

[0053] The microstructure of the GH4141 high-temperature alloy forged bar prepared by the above method is as follows: Figure 2 As shown, the microstructure is uniform, with MC carbides evenly dispersed and without aggregation, while M6C carbides are all precipitated discontinuously in granular form along the grain boundaries. High-temperature notch creep rupture performance tests were conducted at 732℃ / 603MPa, and the fracture times of the bars were 41.2h and 40.0h, respectively, with both fracture locations situated in the smooth section, indicating that the forged bar has no notch sensitivity.

[0054] Comparative Example 1 This comparative example prepared GH4141 alloy bars with a diameter of Φ250mm. Steps A to C were the same as in Example 1, but without the second homogenization heat treatment. Secondary forging was performed directly after step C, and the remaining steps D to H were the same as in Example 1.

[0055] The GH4141 alloy rods prepared in this comparative example, after heat treatment, contained large-sized, incompletely dissolved M6C carbides. After aging, a small amount of fine M6C carbides precipitated at the grain boundaries. The microstructure is shown below. Figure 3 High-temperature notch creep rupture test was conducted at 732℃ / 603MPa. The fracture times of the bars were 20.1h and 14.3h, respectively, and the fracture locations were both at the notch, indicating significant notch sensitivity.

[0056] Comparative Example 2 This comparative example prepares GH4141 alloy bars with a diameter of Φ250mm. Steps A to E are the same as in Example 1. The difference lies in the subsequent final hardening, rapid forging, and radial forging process parameters, which are as follows: F, final forging: The intermediate billet obtained after the second forging is heated to 1100°C and held for 3 hours, and then subjected to a single forging process. The forging deformation is 40% (lower than 60% in Example 1 of this invention). During the forging process, insulation cotton is used to wrap the billet to obtain a quick-forging billet.

[0057] G. Radial forging: The fast forging billet is heated to 1090℃ (lower than 1120℃ in Example 1 of this invention), held for 3 hours, and then subjected to one heat forging. The radial forging deformation is 30%. During radial forging, insulation cotton is used to wrap the billet to obtain the finished forging bar.

[0058] H, Performance heat treatment: The forged bar is subjected to performance heat treatment, and the process is the same as in Example 1, that is: after holding at 1080℃ for 1 hour, it is water-cooled, and then held at 760℃ for 16 hours before air cooling.

[0059] Test Results and Analysis: The GH4141 alloy forged bars prepared by the above process were subjected to microstructure observation and high-temperature notch creep rupture performance testing after performance heat treatment. The results are as follows: Microstructure: After heat treatment, although the primary M6C carbide was completely dissolved, the precipitation behavior of the secondary M6C carbide changed significantly. It did not precipitate discontinuously in granular form along the grain boundaries, but rather randomly precipitated within the grains, at grain boundaries, and around the MC carbide, forming a non-uniform microstructure (see details). Figure 4 ).

[0060] Notch creep performance: High-temperature notch creep performance tests were conducted at 732℃ / 603MPa, with fracture times of 23.3h and 24.7h, respectively. Although the absolute fracture times still met the basic requirements, the fracture locations of both specimens were at the notch, indicating that the forged bar exhibits significant notch sensitivity.

[0061] Compared to Example 1 (same specifications, same chemical composition, and same preceding processes), this comparative example failed to achieve sufficient microstructure refinement and homogenization due to the use of lower heating temperatures and smaller deformation amounts in the final forging and radial forging processes. This directly led to the abnormal precipitation of secondary carbides, thereby inducing notch sensitivity in the material. This demonstrates that the final forging and radial forging process parameters defined in this invention (such as a heating temperature of 1120°C and a large deformation amount) play a crucial role in eliminating the notch sensitivity of the GH4141 alloy.

[0062] Comparative Example 3 This comparative example prepared GH4141 alloy bars with a diameter of Φ250mm. Steps A to G were the same as in Example 1. For performance heat treatment, the solution treatment process was: 1120℃ (higher than the 1070-1100℃ range specified in this invention), held for 1 hour, and then water-cooled; the aging treatment process was: 760℃, held for 16 hours, and then air-cooled.

[0063] The GH4141 alloy forged bars prepared by the above process were subjected to microstructure observation and high-temperature notch creep rupture performance testing after performance heat treatment. The results are as follows: Microstructure: After heat treatment, although the MC carbides in the bar stock remained uniformly dispersed without aggregation, the excessively high solution temperature (1120℃) caused the M6C carbides that should have precipitated in the alloy to completely disappear, failing to form discontinuous granular precipitates at the grain boundaries. Instead, a large number of continuous M6C carbides precipitated at the grain boundaries. 23 C6 carbides (see details) Figure 5 This continuous grain boundary precipitation is extremely detrimental to the plasticity and durability of the material.

[0064] Notch creep performance: High-temperature notch creep performance tests were conducted at 732℃ / 603MPa, and the fracture times decreased sharply to 5.7h and 5.4h, respectively, which are far lower than the levels in Example 1 of this invention (42.8h, 43.4h). Furthermore, the fracture locations of both specimens were at the notch, indicating that the forged bar exhibits extremely significant notch sensitivity.

[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0066] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a notch-free, sensitive GH4141 high-temperature alloy forged bar, characterized in that, Includes the following steps: The GH4141 high-temperature alloy ingot was subjected to a first homogenization heat treatment, pre-forging, a second homogenization heat treatment, a second forging, and subsequent forging to obtain a forged bar. The temperature of the first homogenization heat treatment is 1160-1200℃, and the holding time is 36-48h; The second homogenization heat treatment is performed at a temperature of 1170℃-1190℃ for 10-15 hours. The pre-forging process includes: heating the ingot after the first homogenization heat treatment to 1130-1160℃, holding it at that temperature for 2-3 hours, and then performing at least three upsetting and drawing forging processes to obtain the first intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%. The secondary forging process includes: cooling the intermediate billet after the second homogenization heat treatment to 1130-1160℃ in a furnace, holding it at that temperature for 2-3 hours, and then performing at least four upsetting and drawing forging processes to obtain a second intermediate billet; wherein the upsetting deformation is 15%-35% and the drawing deformation is 20%-40%. The subsequent forging includes a final forging: the second intermediate billet obtained after the second forging is heated to 1100-1120℃, held for 2-3 hours, and then subjected to a single forging process with a deformation of 45%-60%, to obtain a quick-forging billet. The subsequent forging also includes radial forging after the final rapid forging: heating the rapid forging billet to 1100℃-1120℃, holding it for 2-3 hours, and performing one round of radial forging with a deformation of 30%-45% to obtain a forged bar; The preparation method further includes the step of heat treatment of the forged bar: solution treatment and aging treatment are performed sequentially; the solution treatment temperature is 1070-1100℃, and the bar is held at the temperature and then water-cooled; the aging treatment temperature is 750-770℃, and the bar is held at the temperature and then air-cooled.

2. The preparation method according to claim 1, characterized in that, After the first homogenization heat treatment and before pre-forging, a cooling process is also included: the ingot furnace is first cooled to 950-1050℃, and then the ingot is directly transferred to the high-speed forging machine heating furnace for pre-forging heating and heat preservation, or it is air-cooled to room temperature for subsequent use.

3. The preparation method according to claim 1, characterized in that, During the pre-forging, secondary forging, and subsequent elongation forging processes, the billet is wrapped with insulating cotton.

4. The preparation method according to claim 1, characterized in that, The GH4141 high-temperature alloy ingot is prepared using a dual process of vacuum induction melting and vacuum arc remelting.

5. A notch-free, non-sensitive GH4141 high-temperature alloy forged bar, characterized in that, The forged rod is prepared by any one of the preparation methods described in claims 1-4. The chemical composition of the forged rod, by mass percentage, includes: C: 0.06–0.12%, Cr: 18.0–20.0%, Co: 10.0–12.0%, Mo: 9.50–10.50%, Al: 1.4–1.8%, Ti: 3.0–3.5%, B: 0.003–0.010%, Si≤0.5%, Mn≤0.5%, Cu≤0.5%, P≤0.015%, S≤0.015%, Fe≤5.0%, Zr≤0.07%, with the balance being Ni and unavoidable impurities. In the microstructure of the forged rod, M6C carbides are distributed in spherical granular form at the grain boundaries. The forged rod exhibits a high-temperature notch fracture time ≥40 h under 732℃ temperature and 603MPa stress conditions, with all fracture locations located in smooth segments.

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