Inconel 718: properties, composition, uses and standards
Inconel 718 is a age-hardenable nickel–chromium alloy with niobium and molybdenum, chosen for very high strength at temperatures up to about 650 °C. UNS N07718, W.Nr 2.4668, density 8.19 g/cm³.
What is Inconel 718?
Inconel 718 is a age-hardenable nickel–chromium alloy with niobium and molybdenum. Engineers choose it for very high strength at temperatures up to about 650 °C. It is also known as Alloy 718, UNS N07718, W.Nr 2.4668, Precipitation-hardening nickel alloy.
- UNS
- N07718
- W.Nr
- 2.4668
- EN
- NiCr19NbMo
- Aerospace
- AMS 5596 (sheet) · AMS 5662/5663 (bar)
- Trade names
- Inconel 718
- Density
- 8.19 g/cm³
- Melting range
- 1260 – 1336 °C
- Magnetic
- Non-magnetic
Chemical composition and what each element does
| Element | Weight % (producer reference) |
|---|---|
| Nickel (+Co) | 50.00 – 55.00 |
| Chromium | 17.00 – 21.00 |
| Iron | Balance |
| Niobium (+Ta) | 4.75 – 5.50 |
| Molybdenum | 2.80 – 3.30 |
| Titanium | 0.65 – 1.15 |
| Aluminium | 0.20 – 0.80 |
| Cobalt | 1.00 max |
| Carbon | 0.08 max |
| Manganese | 0.35 max |
| Silicon | 0.35 max |
| Phosphorus | 0.015 max |
| Sulphur | 0.015 max |
| Boron | 0.006 max |
| Copper | 0.30 max |
Per Special Metals INCONEL alloy 718 bulletin SMC-045 (2007) — producer reference composition, not a specification requirement; specification limits in ASTM B637-26, B670-25 and A1014/A1014M-26 are pending current standard text.
Niobium forms the gamma-double-prime precipitate that gives 718 its high strength after age hardening.
Keeps very high strength and creep resistance up to about 650 °C.
Its slow ageing response gives good resistance to strain-age cracking during post-weld heat treatment; welding procedure and post-weld treatment still follow the applicable code and specification.
718 is chosen for strength; for corrosion alone, 625 or 825 are usually better value.
Inconel 718 at a glance
See the Inconel 718 product page for every form we supply and its standard.
Mechanical properties
| Specification | Product form | Condition | Requirement values |
|---|---|---|---|
| ASTM B637 (B637-26) | rod, bar, forgings, forging stock | as specified (e.g. solution treated and precipitation hardened) | As specified |
| ASTM B670 (B670-25) | plate, sheet, strip | annealed (per current scope) | As specified |
| ASTM A1014/A1014M (A1014/A1014M-26) | bolting (product types pending) | as specified | As specified |
Numerical requirements are not shown until the current edition of each standard has been verified. Mechanical properties depend on product form, size, condition and heat treatment — state them on the purchase order.
Where Inconel 718 is used
- Oil & gas. Wellhead parts, hangers and high-strength bolting. Industry →
- Aerospace. Turbine discs, casings and fasteners. Industry →
- Power. Gas-turbine and nuclear components. Industry →
- Tooling. Hot-work tooling and springs. Industry →
Welding 718
The matching filler is ERNiFeCr-2 (AWS A5.14). Post-weld solution treatment and ageing restore strength.
Keep heat input moderate and interpass temperature low, clean joints thoroughly, and pickle or passivate after welding where the service is corrosive.
Inconel 718 compared with similar grades
| Grade | PREN | Choose it for |
|---|---|---|
| Inconel 718 | — | Very high strength at temperatures up to about 650 °C |
| Inconel 625 | ≈ 51 | Seawater, high strength and high temperature in one alloy |
| Inconel 600 | — | High-temperature oxidation, caustic and nuclear service |
| Inconel 825 | ≈ 31 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
Inconel 718 standards by product
| Product | Standard |
|---|---|
| Inconel 718 sheet | ASTM B670 · AMS 5596 |
| Inconel 718 plate | ASTM B670 · AMS 5596 |
| Inconel 718 coil | ASTM B670 |
| Inconel 718 pipe & tube | a specification not yet established |
| Inconel 718 fittings | a specification not yet established · a specification not yet established |
| Inconel 718 flanges | project / purchase specification dependent |
| Inconel 718 fasteners | ASTM A1014 (UNS N07718) where specified for applicable bolts and studs — product-type scope pending current standard text; for other types, material may be supplied to ASTM B637 bar where applicable, subject to the purchase specification or project drawing |
Buying Inconel 718: what to specify
- The product standard and the UNS or designation — for example ASTM B670 · AMS 5596 UNS N07718.
- Size, thickness or schedule, and quantity in pieces and kg or metres.
- Heat-treatment condition where the standard offers a choice.
- Certificate: EN 10204 3.1 or 3.2 available on request / as specified in the PO; ask for 3.2 if a third party must witness.
- NACE MR0175 / ISO 15156 compliance if the service contains H₂S.