Inconel 718 and Inconel X-750 are two precipitation hardening members of the same family. X-750 is the older alloy and relies on a different hardening chemistry.
High nickel, low iron
According to our datasheets, nickel + cobalt in X-750 is min 70.0%; in 718 nickel is in the 50.0–55.0% range. Iron changes in parallel: 5.00–9.00% in X-750 against 12.0–24.0% in 718.
The hardening mechanism differs as well. X-750 takes its strength largely from the gamma prime phase formed by 2.25–2.75% titanium and 0.40–1.00% aluminium; niobium + tantalum is only at 0.70–1.20%. In 718 that ratio is reversed: niobium + tantalum 4.75–5.50%, titanium 0.65–1.15%.
The practical result: X-750 shows elasticity at high temperature and resistance to relaxation — which is why it is used for springs, bolt locking devices and sealing elements working in hot zones. 718 gives higher strength and is markedly easier to weld. X-750 also contains no molybdenum, while 718 has 2.80–3.30%.
Comparison in numbers
| PROPERTY | Inconel 718 | Inconel X-750 |
|---|---|---|
| Nickel | 50.0 – 55.0% | min 70.0% (Ni+Co) |
| Chromium (Cr) | 17.0 – 21.0% | 14.0 – 17.0% |
| Iron (Fe) | 12.0 – 24.0% | 5.00 – 9.00% |
| Molybdenum (Mo) | 2.80 – 3.30% | — |
| Niobium + Tantalum | 4.75 – 5.50% | 0.70 – 1.20% |
| Titanium (Ti) | 0.65 – 1.15% | 2.25 – 2.75% |
| Aluminium (Al) | 0.20 – 0.80% | 0.40 – 1.00% |
| Carbon (C) | max 0.08% | max 0.08% |
| Cobalt (Co) | max 1.00% | max 1.00% |
| Copper (Cu) | max 0.30% | max 0.50% |
| UNS | N07718 | N07750 |
| W.Nr (DIN/EN) | 2.4668 | 2.4669 |
| AMS | 5596 · 5663 | 5542 · 5598 · 5667 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Inconel 718 is preferred — turbine discs, highly stressed structural parts, fasteners, welded components. Its strength is higher, it is easier to manufacture, and it is far more common in aerospace specifications.
Inconel X-750 is required — springs working at high temperature, bolt locking elements, turbine seal and clip components, nuclear reactor internals. If the specification calls out AMS 5542 or AMS 5598, the grade being asked for is X-750.
Neighbouring alloys
For higher temperatures, see our Inconel 718 – Waspaloy comparison; for the solid solution alternatives, our Inconel 600 – 625 comparison.
Technical datasheets
Inconel 718 — chemical composition, mechanical values, standard equivalents
Inconel X-750 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.