Inconel X-750
US grade: Inconel X-750 nickel-based high-temperature alloy
China grade: GH145/GH4145
Germany grade: NiCr15Fe7TiAl
France grade: NC15FeTNbA
Japan grade: NCF750
1. Overview of Inconel X-750 nickel-based high-temperature alloy:
Inconel X-750 alloy is primarily a nickel-based high-temperature alloy that is age-hardened with the γ′[Ni3](Al, Ti, Nb)] phase. It has good corrosion resistance and oxidation resistance below 980℃, high strength below 800℃, and good relaxation resistance below 540℃, while also possessing good formability and weldability. This alloy is mainly used to manufacture corrosion-resistant ring parts, structural parts, and bolts that work below 800℃ and require high strength, as well as flat springs and helical springs that work below 540℃ with medium or lower stress and require relaxation resistance. It can also be used to manufacture parts such as gas turbine blades. Available forms include plates, strips, bars, forgings, rings, wires, and pipes.
1. Inconel X-750 material grade: Inconel X-750.
2. Similar grades to Inconel X-750: GH145/GH4145 (China), NiCr15Fe7TiAl (Germany), NC15FeTNbA (France).
3. Technical standards for Inconel X-750 material:
4. Chemical composition of Inconel X-750: see Table 1-1
Table 1-1                                                                 

Note: The Mn and Si content in the table is for bars, forgings, rings, and wires, while for plates, strips, and pipes: ω(Mn)≤0.35%, ω(Si)≤0.35%.
5. Heat treatment system for Inconel X-750: The solution heat treatment system for plates, strips, and pipes is 980℃±15℃, air-cooled. The intermediate heat treatment system for materials and parts can choose the following processes for heat treatment.
(1) Annealing: 955～1010℃, water-cooled.
(2) Annealing before welding for welded parts: 980℃, 1h.
(3) Stress relief annealing for welded parts: 900℃, hold for 2h.
(4) Stress relief annealing: 885℃±15℃, 24h, air-cooled.
6. Specifications and supply status of Inconel X-750: Various specifications of bars, forgings, rings, hot-rolled plates, cold-rolled plates, strips, pipes, and wires can be supplied.
(1) Plates and strips are generally supplied after hot-rolling or cold-rolling, annealing or solution treatment, and pickling and polishing.
(2) Bars, forgings, and rings can be supplied in forged or hot-rolled state; they can also be supplied after solution treatment post-forging; bars can be supplied polished or turned after solution treatment, and when required by the order, they can be supplied in cold-drawn state.
(3) Pipes are supplied after solution treatment and removal of oxide scale.
(4) Wires can be supplied in solution state; for wires with a nominal diameter or thickness below 6.35mm, they can be supplied after solution treatment with 50%～65% cold-drawn deformation; for wires with a nominal diameter or edge length greater than 6.35mm, they are supplied with not less than 30% cold-drawn deformation after solution treatment. For wires with a nominal diameter or edge length not greater than 0.65mm, they are supplied with not less than 15% cold-drawn deformation after solution treatment as required.
7. Melting and casting process of Inconel X-750: The alloy is produced using electric arc furnace with vacuum consumable remelting, vacuum induction with electroslag, electroslag with vacuum consumable remelting, or vacuum induction with vacuum consumable remelting.
8. Application overview and special requirements of Inconel X-750: This alloy is mainly used to manufacture corrosion-resistant flat wave springs, circumferential helical springs, helical compression springs, spring retaining rings, and sealing rings for aircraft engines operating at temperatures below 540℃.
2. Physical and chemical properties of Inconel X-750:
1. Thermal properties of Inconel X-750:
(1) Melting temperature range of Inconel X-750: 1395～1425℃.
(2) Thermal conductivity of Inconel X-750: see Table 2-1.
Table 2-1

(3) Coefficient of linear expansion for Inconel X-750: see Table 2-2.
Table 2-2

2. Density of Inconel X-750: ρ=8.25g/cm³
3. Electrical properties of Inconel X-750: resistivity ρ=1.22×10 at 50℃^-6Ω·m
3. Mechanical properties of Inconel X-750:
1. Mechanical properties at room temperature for strips, plates, and pipes as specified in the technical standards for Inconel X-750: see Table 3-1.
Table 3-1

Note: The delivery state is solution treated at 980℃±15℃, held for an appropriate time, air cooled or fast cooled, and scale removed.
2. Mechanical properties at room temperature for wires as specified in the technical standards for Inconel X-750: see Table 3-2.
Table 3-2

Note: In the delivery state, wires are solution treated at a certain temperature within 1090～1200℃ before cold drawing to finished products, and then cold drawn according to the following specifications;
Class A: Wires with nominal diameter or edge length not exceeding 6.35mm, cold drawn deformation amount is 50%～65%; wires with nominal diameter or edge length greater than 6.35mm, cold drawn deformation amount is more than 30%.
Class B: Wires with nominal diameter or edge length not exceeding 0.65mm, cold drawn deformation amount is about 15%.
3. The durability performance specified in the standards for Inconel X-750 bars, forgings, and rings: see Table 3-3
Table 3-3

4. Inconel X-750 microstructure:
1. Inconel X-750 phase transformation temperature: The precipitation temperature of the γ′ phase is about 600℃, the peak precipitation is about 800℃, it starts to dissolve at 900℃, and is almost completely dissolved at 970℃.
2. Inconel X-750 time-temperature-structure transformation curve.
3. Inconel X-750 alloy microstructure: After standard heat treatment, the structure consists of γ matrix, Ti(C, N), Nb(C, N), M23C6carbides and γ′[Ni3(Al, Ti, Nb)] phase, with a γ′ content of about 14.5%, which is the main strengthening phase of the alloy.
5. Inconel X-750 process performance and requirements:
1. Inconel X-750 forming performance: The forging temperature of the alloy is easy to form between 1220～950℃. The heating temperature for steel ingot open die forging can be at 1200℃. To obtain good structure and performance for the final forged parts or bars, subsequent forging heating should be done at relatively lower temperatures. The final forging temperature should not be lower than 950℃. This alloy should undergo solution treatment after severe forming processes.
2. Inconel X-750 welding performance: The alloy has good welding performance and can be welded in various ways, but it is difficult to perform fusion welding on large cross-section parts, while small cross-section parts and thin plates have better welding performance. Welding must be performed after annealing or solution treatment, and post-weld stress relief treatment should be carried out at 980℃ for 0.5h or 900℃ for 2h. Subsequent aging treatment of welded assemblies can achieve strength close to that of fully heat-treated states.
3. Inconel X-750 part heat treatment process: The heat treatment of parts should be carried out in a sulfur-free neutral or reducing atmosphere to avoid sulfidation. Parts should avoid "heat-cool" treatment between 870～650℃. For large cross-section parts, to prevent cracking, they should be air-cooled after solution treatment. The final heat treatment of finished parts is as follows:
(1) For components working above 600℃, requiring optimal long-term creep performance:
Solution: 1150℃±15℃, holding for 2-4h, air cooling;
Aging: 845℃±15℃, holding for 24h, air cooling + 705℃±15℃, holding for 24h, air cooling.
(2) For components working below 600℃, requiring optimal room temperature and high-temperature tensile performance:
Solution: 980℃±15℃, holding for 1h, air cooling;
Aging: 730℃±15℃, holding for 8h, cooling to 620℃±10℃ at 50℃/h, holding for 8h, air cooling.
(3) Ring parts generally adopt the following heat treatment system:
Solution: 1095℃±15℃, holding for 2-4h, air cooling;
Aging: 845℃±15℃, holding for 24h, air or furnace cooling to +705℃±15℃, holding for 20h, air cooling.
(4) For bars and forgings used at temperatures below 600℃, the following heat treatment system is adopted: Homogenization: 885℃±15℃, holding for 24h, air cooling; Aging: 705℃±15℃, holding for 20±1h, air cooling.

(5) Annealed plates and strips, as well as plates and wires used for springs, can be treated as follows: Aging:

1) 705℃±15℃, holding for 22h, air cooling;

2) 760℃±10℃, holding for 1h, air cooling. Solution: 980℃±15℃, holding for 1h, air cooling; Aging: 730℃±10℃, holding for 8h, cooling to +620℃±10℃ at 50℃/h, holding for 8h, air cooling.
4. Inconel X-750 cutting and grinding performance: The alloy can be machined in various states, with good machining performance in annealed or solution-treated states.
5. Inconel X-750 varieties, specifications, and supply status:
1. Variety classification: Inconel X-750 seamless pipes, Inconel X-750 steel plates, Inconel X-750 round steel, Inconel X-750 forgings, Inconel X-750 flanges, Inconel X-750 rings, Inconel X-750 welded pipes, Inconel X-750 steel strips, Inconel X-750 wires and matching welding materials.
2. Delivery status: Seamless pipes: solution + acid pickling, length can be customized; plates: solution, acid washing, edge cutting; welded pipes: solution acid pickling + RT% flaw detection, forgings: annealing + turning; bars in forged state, surface polished or turned; strips delivered after cold rolling, solution soft state, and descaling; wires delivered in solution acid-washed coil or straight bar form, solution straight bar finely polished.