Haynes 25 (also known as L-605) and Inconel 625 are both solid solution hardened alloys and both work at high temperature. The fundamental difference is what the base metal is: one is cobalt based, the other nickel based.
What does a cobalt matrix bring?
According to our datasheets, the main element of Haynes 25 is cobalt; alongside it are ~20% chromium, ~15% nickel and ~10% tungsten. Inconel 625 is nickel based with min 58% nickel; chromium 20.0–23.0%, molybdenum 8.00–10.0%, niobium + tantalum 3.15–4.15%.
A cobalt matrix has three clear advantages. The first is temperature: cobalt-based alloys retain their strength at higher temperatures than nickel-based ones. Our datasheet gives Haynes 25 strength up to 980 °C and creep stability up to 815 °C.
The second is wear and galling resistance: cobalt alloys are far more resistant to seizing and tearing under sliding contact. The third is sulphur-bearing environments: cobalt is more resistant to sulphidation corrosion than nickel.
The advantage of Inconel 625 is in aqueous corrosion — thanks to molybdenum and niobium it is well ahead of Haynes 25 in seawater and acid environments. It is also far more economical and easier to source.
Comparison in numbers
| PROPERTY | Haynes 25 (L-605) | Inconel 625 |
|---|---|---|
| Base metal | Cobalt | Nickel |
| Cobalt (Co) | Balance | max 1.00% |
| Nickel (Ni) | ~15% | min 58.0% |
| Chromium (Cr) | ~20% | 20.0 – 23.0% |
| Tungsten (W) | ~10% | — |
| Molybdenum (Mo) | — | 8.00 – 10.0% |
| Niobium + Tantalum | — | 3.15 – 4.15% |
| Iron (Fe) | Trace | max 5.00% |
| Tensile strength (room temp.) | ~960 MPa | — |
| Yield strength (room temp.) | ~400 MPa | — |
| Service temperature | strength up to 980 °C | — |
| Creep resistance | stable up to 815 °C | — |
| Hardening mechanism | Solid solution | Solid solution |
| UNS | R30605 | N06625 |
| AMS / ASTM | 5537 · 5759 · ASTM F90 | 5599 · 5666 · 5837 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Haynes 25 is required — gas turbine combustion chambers and transition pieces, afterburner components, high-temperature springs, sliding contact surfaces, medical implant and stent applications (ASTM F90 covers that use). Parts carrying load above 900 °C or exposed to wear.
Inconel 625 is required — seawater and chemical environment equipment, exhaust and fuel systems, welded structures, offshore pipelines. If there is aqueous corrosion and the temperature is below 900 °C, 625 is both better and far more economical.
Neighbouring alloys
For nickel-based alternatives at high temperature, see our Hastelloy X – Inconel 625 and Nimonic 80A – Waspaloy comparisons.
Technical datasheets
Haynes 25 — chemical composition, mechanical values, standard equivalents
Inconel 625 — 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.