What is Inconel 718, and why do engineers specify it?
Inconel 718 is a nickel-based superalloy strengthened by γ″ (gamma double-prime) precipitates of Ni₃Nb. Unlike most superalloys that lose strength at aging temperatures below 600°C, 718's γ″ structure remains stable up to about 650°C, giving it an unusual combination of high strength and weldability at elevated temperature.
For procurement and design engineers, the reason to choose 718 is usually one of these:
- High-temperature strength to 650°C without losing tensile properties — jet engine disks, turbocharger wheels, rocket injector plates.
- Cryogenic toughness — 718 retains ductility down to −253°C, making it the workhorse of liquid-oxygen and liquid-hydrogen systems.
- Corrosion resistance in sour gas, seawater, and oxidizing acids — standard for subsea connectors, downhole tools, and chemical process valves.
- Non-magnetic behavior — useful for MRI-compatible and downhole measurement tools.
The trade-off is cost and machinability. Raw 718 bar stock costs roughly 15–20× more than 6061 aluminum by weight, and cuts at about one-tenth the surface speed. On a typical bracket, expect the 718 part to cost 8–12× the aluminum equivalent — before heat treatment.
Important — aged vs solution condition: we supply 718 in either solution annealed (AMS 5662, softer, easier to machine, aged after machining) or aged/precipitation hardened (AMS 5663, full strength, more expensive to cut). Tell us which you need in your RFQ, because it affects cost, lead time, and achievable tolerance. When in doubt, specify AMS 5662 + post-machining age — this is the common aerospace pattern.