Drawing No. EH–MT–017 // Engineering Materials
INCONEL 718 Properties
Reviewed September 2026
INCONEL 718 is a precipitation-hardenable nickel superalloy used where high strength, fatigue/creep resistance and corrosion resistance are required over a broad temperature range.
Representative properties
The stated basis, temperature and direction are part of the value. Switch units without changing the physical reference.
What changes these properties?
Engineering variability
- Heat treatment strongly controls γ′/γ″ strengthening and therefore yield/tensile properties.
- Elastic properties are anisotropic at the single-crystal grain level; wrought product values are engineering averages.
- Thermal conductivity is low compared with steels and rises with temperature.
- For turbine/aerospace design, use product-form-specific fatigue, creep and rupture data.
Selection note
A benchmark aerospace and high-temperature alloy for turbine disks, fasteners, rocket components, springs and high-strength corrosion-resistant hardware.
Where a property is shown as qualitative rather than numeric, that is intentional: the selected source or the material physics does not justify a single comparable scalar.
Inconel 718 in practice
The precipitation-hardened nickel superalloy that dominates hot rotating hardware, and the one whose properties depend entirely on heat treatment.
Where it is specified
718 accounts for a large share of gas turbine mass: discs, blades, casings, shafts, seals and fasteners in the compressor and turbine sections. Beyond aerospace it appears in rocket engine turbopumps, subsea wellhead and completion equipment, downhole tools, and high-temperature bolting.
It is specified where 650–1000 MPa yield strength must survive at 500–650 °C while resisting oxidation and creep — conditions in which any steel would have lost most of its strength.
Chosen over what
Against 625: roughly twice the strength after ageing, but it must be aged, and weld repair requires re-solution and re-age. Use 625 where corrosion resistance and fabricability dominate, 718 where strength at temperature does.
Against Waspaloy or René 41: 718's slow gamma-double-prime precipitation kinetics make it far more weldable, because the alloy does not age during the weld thermal cycle and so resists strain-age cracking. That single metallurgical fact is why 718 became the most-used superalloy.
Against titanium: 718 is twice as dense but usable far above titanium's 400–500 °C ceiling, and is not subject to titanium fire risk in compressors.
How it fails
Creep and stress rupture above about 650 °C, where the strengthening gamma-double-prime phase coarsens and transforms to the stable, non-strengthening delta phase. This sets a hard service ceiling around 650–700 °C.
Fatigue from inclusions and surface condition. In discs, life is governed by the largest defect present, which is why premium melting practice (VIM followed by VAR, sometimes triple melt) is mandated — the standard is set by what must not be in the material.
Hydrogen embrittlement in subsea and sour service at high hardness, which is why NACE limits hardness for those applications.
Strain-age cracking is comparatively unlikely but not impossible in heavily restrained weldments given an unfavourable thermal history.
Fabrication notes
Machinability is very poor, around 10–15% of B1112, and worse after ageing. Solution-treated material is machined first where possible, with ceramic or whisker-reinforced tooling at high speed, or carbide at low speed with heavy coolant. Tool wear is notching at the depth-of-cut line, driven by work hardening.
Weldability is good for a precipitation-hardened superalloy, which is the whole point of the alloy. Welding is normally done in the solution-treated condition, followed by a full solution and double-age cycle — typically 954–1065 °C solution, then 718 °C and 621 °C ageing steps.
Delta phase control during forging governs grain size and notch sensitivity; the heat treatment specified must match the application, and AMS 5662 and AMS 5663 material is not interchangeable with alternative cycles.
Specifications and standards
AMS 5662/5663/5664 (bar and forgings), AMS 5596/5597 (sheet); ASTM B637 for precipitation-hardened bar; UNS N07718; AWS A5.14 ERNiFeCr-2 filler; API 6A718 for subsea wellhead equipment; NACE MR0175/ISO 15156 hardness limits.
References
Special Metals INCONEL alloy 718 bulletin; Reed, The Superalloys: Fundamentals and Applications; ASM Handbook Vol. 4E, Heat Treating of Nonferrous Alloys.
How to interpret this material
Stiffness
Young’s modulus describes elastic stiffness. For crystals and composites, orientation can make one scalar modulus only a directional reference.
Strength / failure
Ductile metals can use yield and tensile strength. Brittle ceramics/semiconductors and anisotropic composites require fracture, flexural or directional strength descriptions instead.
Thermal response
Conductivity, heat capacity and expansion are temperature dependent. The last column is a melting or transition descriptor only where that physical concept is appropriate.
Technical sources
The database favors manufacturer, industry, government or academic technical references and labels secondary condition-specific datasets when a primary source does not expose a complete property set.