GH4169
Chinese grade: GH4169/GH169 high-temperature alloy
American grade: Inconel 718/UNS NO7718
French grade: NC19FeNb
1.Overview of GH4169 (Inconel 718, N07718) high-temperature alloy:
The GH4169 alloy is a nickel-based high-temperature alloy that is strengthened by the precipitation of body-centered tetragonal γ" and face-centered cubic γ′ phases. It has good comprehensive performance in the temperature range of -253 to 700°C, with the yield strength below 650°C ranking first among deformed high-temperature alloys. It also exhibits good fatigue resistance, radiation resistance, oxidation resistance, corrosion resistance, as well as good processing performance, welding performance, and long-term organizational stability, making it capable of manufacturing various complex-shaped components. It has been widely used in aerospace, nuclear energy, and petroleum industries within the aforementioned temperature range.
Another characteristic of this alloy is that its microstructure is particularly sensitive to thermal processing. By mastering the precipitation and dissolution laws of phases in the alloy and the interrelationship between microstructure, processing, and performance, reasonable and feasible process specifications can be formulated according to different usage requirements, thus obtaining various parts that meet different strength levels and usage requirements. The supplied varieties include forgings, forged bars, rolled bars, cold-rolled bars, discs, rings, plates, strips, wires, pipes, etc. It can be made into discs, rings, blades, shafts, fasteners, elastic components, plate structural parts, casings, and other components for long-term use in aviation.
1. GH4169 material grade: GH4169 (GH169)
2. Similar grades to GH4169: Inconel 718 (USA), NC19FeNb (France)
3. Technical standards for GH4169 material:
4. Chemical composition of GH4169: The chemical composition of this alloy is divided into three categories: standard composition, high-quality composition, and high-purity composition, as shown in Table 1-1. The high-quality composition reduces carbon and increases niobium based on the standard composition, thereby reducing the amount of niobium carbide, decreasing fatigue sources, and increasing the number of strengthening phases, improving fatigue resistance and material strength. At the same time, it reduces harmful impurities and gas content. The high-purity composition reduces the content of sulfur and harmful impurities based on the high-quality standard, improving material purity and comprehensive performance.
For the nuclear energy application of GH4169 alloy, the boron content must be controlled (other elemental compositions remain unchanged), and the specific content is determined through negotiation between the supply and demand parties. When ω (B) ≤ 0.002%, to distinguish it from the GH4169 alloy used in the aerospace industry, the alloy grade is designated as GH4169A.
Table 1-1^[1]                                                                  %
 

5. GH4169 heat treatment system: The alloy has different heat treatment systems to control grain size, morphology, distribution, and quantity of the δ phase, thereby obtaining different levels of mechanical properties. The alloy heat treatment system is divided into three categories:
(1) (1010～1065)℃±10℃, 1h, oil cooling, air cooling, or water cooling + 720℃±5℃, 8h, cool in the furnace to 620℃±5℃ at 50℃/h, 8h, air cool.
Materials treated by this system have coarsened grains, with no δ phase at the grain boundaries or within the grains, exhibiting notch sensitivity, but are beneficial for improving impact performance and resisting low-temperature hydrogen embrittlement.
(2) (950～980)℃±10℃, 1h, oil cooling, air cooling, or water cooling + 720℃±5℃, 8h, cool in the furnace to 620℃±5℃ at 50℃/h, 8h, air cool.
Materials treated by this system contain δ phase, which helps eliminate notch sensitivity. This is the most commonly used heat treatment system, also known as the standard heat treatment system.
(3) 720℃±5℃, 8h, cool in the furnace to 620℃±5℃ at 50℃/h, 8h, air cool.
After treatment by this system, the δ phase in the material is reduced, which can improve the strength and impact performance of the material. This system is also known as the direct aging heat treatment system.
6. GH4169 varieties, specifications, and supply status: Forgings (discs, integral forgings), cakes, rings, bars (forged bars, rolled bars, cold drawn bars), plates, wires, strips, pipes, fasteners of different shapes and sizes, elastic elements, etc., can be supplied, with delivery status agreed upon by both parties. Wire materials are delivered in coil form as per the agreed delivery status.
7. GH4169 melting and casting process: The alloy's smelting process is divided into three categories: vacuum induction melting with electroslag remelting; vacuum induction melting with vacuum arc remelting; vacuum induction melting with electroslag remelting plus vacuum arc remelting. The required smelting process can be selected based on the usage requirements of the parts to meet application needs.
8. GH4169 application overview and special requirements: Used in the manufacture of various stationary and rotating parts in aviation and aerospace engines, such as discs, rings, casings, shafts, blades, fasteners, elastic elements, gas ducts, sealing elements, and welded structural parts; used in the manufacture of various elastic elements and frames for nuclear energy applications; used in the manufacture of parts and other components for the oil and chemical industries.
In recent years, based on the continuous deepening of research on this alloy and the expanding applications of this alloy, many new processes have been developed to improve quality and reduce costs: vacuum arc remelting uses helium gas cooling technology, effectively reducing niobium segregation; injection molding technology is used to produce rings, reducing production costs and shortening production cycles; superplastic forming technology is used to expand the production range of products.
二、GH4169 (Inconel 718, N07718) high-temperature alloy physical and chemical properties:
1. GH4169 thermal properties:
(1) GH4169 melting temperature range: 1260–1320℃.
(2) GH4169 thermal conductivity: see Table 2-1.
Table 2-1
 

(3) GH4169 specific heat capacity: see Table 2-2.
(4) GH4169 linear expansion coefficient: see Table 2-3.
2. GH4169 density: ρ=8.24g/cm.³。
3. GH4169 electrical properties: see Table 2-2.
Table 2-2
 

 Table 2-3
 

4. GH4169 magnetic properties: The alloy is non-magnetic.
5. GH4169 chemical properties:
6. GH4169 oxidation resistance: The oxidation rate after 100 hours of testing in air is shown in Table 2-4.
Table 2-4
 

三、GH4169 (Inconel 718, N07718) high-temperature alloy performance requirements:
1. Due to the high niobium content in the GH4169 alloy, the segregation of niobium in the alloy is directly related to the metallurgical process. The melting speed of electroslag remelting and vacuum arc melting, as well as the quality state of the electrode rods, directly affect the quality of the material. A fast melting speed can easily form niobium-rich black spots; a slow melting speed can form niobium-poor white spots; poor surface quality of the electrode rods and internal cracks can easily lead to the formation of white spots. Therefore, improving the quality of the electrode rods, controlling the melting speed, and increasing the solidification rate of the ingots are key factors in the smelting process. To avoid excessive segregation of elements in the ingots, the diameter of the ingots used should not exceed 508mm. The homogenization process must ensure that the L phase in the ingots is completely dissolved. The time for two-stage homogenization of the ingots and secondary homogenization of the intermediate billets is determined based on the diameter of the ingots and intermediate billets. The control of the homogenization process is directly related to the segregation degree of niobium in the material. Currently, the homogenization process used in production is 1160℃ for 20h + 1180℃ for 44h, which is still insufficient to eliminate segregation in the center of the ingots. Therefore, the following processes are recommended:
(1) 1150℃~1160℃, 20h~30h + 1180℃~1190℃, 110h~130h;
(2) 1160℃, 24h + 1200℃, 70h.
2. The alloy after homogenization treatment has good hot working performance. The heating temperature for opening the ingot should not exceed 1120℃. The forging process of the forgings should be determined based on the usage conditions and application requirements of the forgings, in conjunction with the conditions of the production plant. During the opening and production of forgings, the intermediate annealing temperature and final temperature must be determined according to the organizational state and performance required for military parts. Generally, the final temperature for forging should be controlled between 930℃ and 950℃. The forging temperature and deformation degree for various types of forgings are shown in Table 3-1.
Table 3-1