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Inconel 718 (UNS N07718) is a nickel-chromium superalloy whose strength comes from precipitation hardening — nano-scale γ″ (Ni₃Nb) and γ′ particles block dislocations.
Its signature age heat treatment (AMS 5662) is ~718 °C for 8 h + 621 °C for 8 h after solution treatment; the “718” name is tied to that aging temperature.
It serves aerospace (turbine disks, shafts, blades, rocket parts) and nuclear (fasteners, springs, control-rod drive mechanisms, fuel hardware).
It keeps useful strength from cryogenic −423 °F up to about 1300 °F.
It is readily weldable, including autogenously in thin section, and is qualified to ASTM/AMS specs.
JN inconel 718 product forms include forgings, round bars, flanges, plates, strips, pipe fittings, tubes and fasteners.
Inconel 718 Similar Grades
GH4169, GH169 (China)
NC19FeNb (France)
NiCr19Fe19Nb5, Mo3 (Germany)
NA 51 (UK)
Inconel718, UNS NO7718 (USA)
NiCr19Nb5Mo3 (ISO)
Grade | C≤ | Mn≤ | Si≤ | S≤ | Cu≤ | Ni | Cr | Co≤ | Mo | Ti | Al | Fe | Nb+Ta | P≤ | B≤ | Ti |
Inconel 718 | 0.08 | 0.35 | 0.35 | 0.015 | 0.30 | 50.0-55.0 | 17.0-21.0 | 1.0 | 2.8-3.3 | 0.65-1.15 | 0.2-0.8 | Remainder | 4.75-5.5 | 0.015 | 0.006 | 0.65-1.15 |
Mechanical properties | Tensile, min, ksi[MPa] | Yield, min, ksi[MPa] | Elongation, %(min) |
Alloy 718 | 185[1275] | 150[1034] | 12 |
STANDARD | WERKSTOFF NR. | UNS | JIS |
Inconel 718 | 2.4668 | N07718 | NCF 718 |
718 is strengthened by precipitation (age) hardening: nano-scale gamma double-prime (γ″, Ni₃Nb) and gamma prime (γ′, Ni₃(Al,Ti)) particles form inside the grains and pin dislocations, so the metal resists deformation.
The three strengthening players
Gamma double-prime (γ″, Ni₃Nb): the primary strengthener. It has a body-centered tetragonal shape that is exceptionally effective at blocking dislocation motion. This is what gives 718 its signature strength.
Gamma prime (γ′, Ni₃(Al,Ti)): a co-strengthener that works alongside γ″, contributing additional hardness and high-temperature stability.
Carbides and delta (δ) phase: niobium/titanium carbides at grain boundaries help stability; a controlled amount of δ phase (also Ni₃Nb) can improve transverse properties, but too much signals over-aging and lowers strength.
Because the strength comes from these precipitates, 718 stays tough even at very high strength levels, which is why engineers trust it for rotating and safety-critical parts.
High temperature strength: The alloy can maintain good strength and toughness at temperatures up to about 700°C, mainly due to its internal stable γ' phase and γ'' phase structure, which can effectively resist deformation and fracture at high temperatures.
Low temperature stability: Even at extremely low temperatures, Inconel 718 can maintain its excellent physical and mechanical properties, which makes it also have excellent application performance in low temperature environments.
Excellent welding and processing: The alloy has good weldability and processing, whether in the annealed state or the aged state, it can be welded and machined in various forms to meet the manufacturing needs of complex components.
Excellent corrosion resistance: Inconel 718 has good tolerance to a variety of corrosive environments, including oxidizing, reducing and salt spray environments, which enables it to maintain long-term stability and reliability in harsh environments.
Product | Standard | Show |
Inconel 718 Bars | ASTM B637 / AMS 5662 / AMS 5663 / AMS 5664 / PWA 1009 / PWA 1010 / GE B50TF15 |  |
Inconel 718 Sheet and Plate | ASTM B670 / AMS 5596 / AMS 5597 / ASTM B637 |  |
Inconel 718 Tube | AMS 5589 / AMS 5590 |  |
Inconel 718 Pipe | AMS 5589 / AMS 5590 |  |
Inconel 718 Forging | ASTM B637 / AMS 5562 / AMS 5663 / AMS 5664 / PWA 1009 / PWA 1010 / GE B50TF15 |  |
The standard cycle AMS 5662 is a solution treatment near 955–982 °C followed by a two-step age: ~718 °C for 8 h, furnace cool to 621 °C, hold 8 h, then air cool. This grows the γ″/γ′ precipitates that create the strength.
| Step | Temperature | Time & cooling | Purpose |
|---|---|---|---|
| Solution treatment | 955–982 °C (1750–1800 °F) | Hold, then rapid cool (water quench or fast air) | Dissolve Nb/Ti/Al uniformly; set grain structure |
| Age 1 | 718 °C (1325 °F) | 8 hours | Nucleate and grow γ″ and γ′ |
| Age 2 | 621 °C (1150 °F) | Furnace cool from 718 °C, hold 8 hours, air cool | Complete precipitation; balance strength & toughness |
Inconel 718 is a workhorse of aviation and space because it keeps high strength from cryogenic to ~650 °C, resists fatigue and creep, and welds well — ideal for engines, airframes, and rockets.
| Segment | Typical components | Why 718 |
|---|---|---|
| Jet / turbine engines | Turbine disks, shafts, blades, spacers, seals, casings, mounts | High strength + creep/fatigue resistance at engine temperatures |
| Aircraft structures | Landing-gear parts, fittings, springs, fasteners | Strength-to-weight and toughness |
| Rocket & space | Liquid-fuel engine parts, manifolds, nozzles, cryogenic tanks/LOX hardware | Strength at −253 °C (LOX) and weldability in aged condition |
| Thrust systems | Thrust reversers, exhaust components | Creep resistance and oxidation resistance |
In nuclear plants 718 is chosen for fasteners, springs, control-rod drive mechanisms, and fuel-assembly hardware because it combines high strength, resistance to stress-corrosion cracking in hot water, good irradiation behavior, and low activation.
| Component | Why 718 is used |
|---|---|
| Control-rod drive mechanisms (CRDM) | High strength and dimensional stability under load and temperature |
| Fasteners & studs | Strength plus resistance to stress-corrosion cracking in high-temperature water |
| Springs & resilient parts | Strength and fatigue resistance in confined spaces |
| Fuel-assembly hardware & spacers | Creep resistance and low activation (low Co limits Co-60) |
| Research & fusion reactors | Irradiation tolerance; also used in fusion structural components |
Cryogenic engineering
Acid environment
Nuclear Engineering
Steam turbine
Liquid fuel rocket
718 resists oxidation to ~980 °C (1800 °F) and performs well in many corrosive media; its high nickel content gives good resistance to chloride stress-corrosion cracking. It is readily weldable, including autogenously in thin section.
Oxidation: stable chromium-rich film protects up to roughly 980 °C (1800 °F).
General & salt-spray corrosion: good in oxidizing, reducing, and salt environments; better than 300-series stainless in many chloride settings.
Chloride stress-corrosion cracking: resisted thanks to high nickel — unlike 316L, which can crack in hot chlorides.
Weldability: welded by GTAW/SMAW and similar processes in solution-annealed or aged condition; low susceptibility to strain-age cracking with a qualified procedure. Thin tube/pipe can be welded autogenously (no filler) for a clean bore — see our Inconel 625 guide for the principle.
Q: What is Inconel 718 used for?
A: Inconel 718 is used where high strength and reliability matter most: aerospace turbine disks, shafts, blades, and rocket-engine parts; nuclear fasteners, springs, control-rod drive mechanisms, and fuel-assembly hardware; plus cryogenic, oil & gas, and high-temperature industrial components.
Q: How does Inconel 718 get its high strength?
A: It is strengthened by precipitation hardening. During aging, nano-scale gamma double-prime (γ″, Ni₃Nb) particles and gamma prime (γ′, Ni₃(Al,Ti)) particles form inside the grains and block dislocations from moving, which is what makes the alloy so strong yet tough.
Q: What is the heat treatment for Inconel 718?
A: The standard cycle (AMS 5662) is a solution treatment near 955–982 °C (1750–1800 °F) followed by a two-step age: about 718 °C (1325 °F) for 8 hours, furnace cool to 621 °C (1150 °F), hold 8 hours, then air cool. This precipitates the strengthening phases.
Q: Is Inconel 718 weldable?
A: Yes. Inconel 718 can be welded in the solution-annealed or fully aged condition by GTAW/SMAW and other processes. With a qualified procedure it has low susceptibility to strain-age cracking; thin sections can even be welded autogenously without filler.
Q: Inconel 718 vs Inconel 625 — which should I choose?
A: Choose 718 when strength and stiffness dominate (aerospace and nuclear structures). Choose 625 when corrosion — especially seawater pitting, crevice attack, and chloride stress-cracking — is the primary concern. 316L is the lower-cost option for mild duty.
Q: Can Inconel 718 be used in nuclear applications?
A: Yes. Its high strength at operating temperature, resistance to stress-corrosion cracking in high-temperature water, good irradiation behavior, and relatively low cobalt content (which limits activation) make it a common choice for fasteners, springs, control-rod drive mechanisms, and fuel-assembly hardware.
Q: What temperature range does Inconel 718 cover?
A: It keeps useful strength from cryogenic temperatures as low as −423 °F (−253 °C), such as liquid-oxygen service, up to about 1300 °F (704 °C); it resists oxidation up to roughly 1800 °F (980 °C).
Q: What specifications cover Inconel 718?
A: Bars and forgings: ASTM B637 / AMS 5662 / 5663 / 5664. Sheet and plate: ASTM B670 / AMS 5596 / 5597. Tube and pipe: AMS 5589 / 5590. The universal grade designation is UNS N07718 (W.Nr. 2.4668).
