Hastelloy C-276 and Hastelloy C-22 are the two most widely used members of the nickel–chromium–molybdenum family. Both were developed for the most demanding environments in the chemical industry. The choice between them is made by asking whether the environment is oxidising or reducing.
Chromium, or molybdenum?
According to our datasheets, molybdenum in C-276 is 15–17% and chromium 14.5–16.5%. In C-22 that balance is reversed: molybdenum falls to 12.5–14.5% while chromium rises to 20.0–22.5%.
This is not a simple preference but a design decision aimed at two different corrosion mechanisms. Molybdenum provides protection in reducing environments (hydrochloric acid, sulphuric acid, phosphoric acid). Chromium is effective in oxidising environments (nitric acid, chlorine-bearing oxidising solutions, wet chlorine gas).
The high chromium of C-22 gives it the wider working window of the two — it performs reasonably in both oxidising and reducing conditions. C-276 is the stronger on the reducing side. Tungsten is present in both: 3.0–4.5% in C-276 and 2.5–3.5% in C-22.
Another difference is in iron: 4.0–7.0% in C-276 and 2.0–6.0% in C-22. C-22 also has tighter impurity limits (phosphorus and sulphur max 0.02%; 0.04% and 0.03% in C-276).
Comparison in numbers
| PROPERTY | Hastelloy C-276 | Hastelloy C-22 |
|---|---|---|
| Chromium (Cr) | 14.5 – 16.5% | 20.0 – 22.5% |
| Molybdenum (Mo) | 15 – 17% | 12.5 – 14.5% |
| Tungsten (W) | 3.0 – 4.5% | 2.5 – 3.5% |
| Iron (Fe) | 4.0 – 7.0% | 2.0 – 6.0% |
| Cobalt (Co) | max 2.5% | max 2.5% |
| Carbon (C) | max 0.01% | max 0.015% |
| Manganese (Mn) | max 1.00% | max 0.5% |
| Silicon (Si) | max 0.08% | max 0.08% |
| Phosphorus (P) | max 0.04% | max 0.02% |
| Sulphur (S) | max 0.03% | max 0.02% |
| Vanadium (V) | max 0.35% | max 0.35% |
| UNS | N10276 | N06022 |
| W.Nr (DIN/EN) | 2.4819 | 2.4602 |
| EN chemical symbol | NiMo16Cr15W | NiCr21Mo14W |
| AMS | 5530 · 5750 | 5766 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Hastelloy C-276 is preferred — hydrochloric and sulphuric acid processes, fluids containing sulphur compounds, pulp bleaching, waste treatment, flue gas desulphurisation. Anywhere reducing conditions dominate. If the specification calls out AMS 5530 or AMS 5750, this is the grade being asked for.
Hastelloy C-22 is required — processes where oxidising and reducing conditions alternate, nitric + hydrofluoric acid mixtures, wet chlorine environments, pharmaceutical and agrochemical reactors. Where the environment is unknown or variable, C-22 is the safer choice.
The other members of the family
There is Hastelloy C-2000, whose acid resistance is widened further by a copper addition, and Hastelloy B-3, developed for purely reducing environments. For high-temperature applications, Hastelloy X is used.
Technical datasheets
Hastelloy C-276 — chemical composition, mechanical values, standard equivalents
Hastelloy C-22 — 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.