Hastelloy B-3 and Hastelloy C-276 are two different families under the same brand. If the choice between them is made wrongly the equipment can be lost within weeks — because one contains no chromium and the other does, and that makes a vital difference in oxidising environments.
Chromium, or no chromium?
According to our datasheets, Hastelloy B-3 has nickel at min 65%, molybdenum at ~28.5% and chromium at max 1.5% — that is, practically none. In C-276 chromium is 14.5–16.5% and molybdenum 15–17%.
Molybdenum provides superior protection in reducing environments (especially hydrochloric acid at every concentration and temperature). The very high molybdenum of B-3 makes it unique in that field; no chromium-bearing alloy gives the same performance.
But the absence of chromium carries a price: B-3 corrodes rapidly in oxidising conditions. Even the presence of oxidising impurities such as iron(III) or copper(II) ions in the acid increases the corrosion rate dramatically. C-276, thanks to its chromium, behaves in a balanced way in both oxidising and reducing conditions.
B-3 was developed to remedy the thermal stability problems of its predecessor B-2; it is far more resistant to phase transformation during welding and heat treatment.
Comparison in numbers
| PROPERTY | Hastelloy B-3 | Hastelloy C-276 |
|---|---|---|
| Nickel (Ni) | min 65% | 51 – 63.5% |
| Molybdenum (Mo) | ~28.5% | 15 – 17% |
| Chromium (Cr) | max 1.5% | 14.5 – 16.5% |
| Tungsten (W) | — | 3.0 – 4.5% |
| Iron (Fe) | max 1.5% | 4.0 – 7.0% |
| Cobalt (Co) | max 3% | max 2.5% |
| Manganese (Mn) | max 3% | max 1.00% |
| Carbon (C) | max 0.01% | max 0.01% |
| Silicon (Si) | max 0.1% | max 0.08% |
| Titanium (Ti) | max 0.2% | — |
| Aluminium (Al) | max 0.5% | — |
| UNS | N10675 | N10276 |
| W.Nr (DIN/EN) | 2.4600 | 2.4819 |
| EN chemical symbol | NiMo29Cr | NiMo16Cr15W |
| AMS | — | 5530 · 5750 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Hastelloy B-3 is required — hydrochloric acid at every concentration, sulphuric acid at boiling temperature, phosphoric acid, acetic and formic acid processes, hydrogen chloride production. Provided there is no oxidising agent in the environment.
Hastelloy C-276 is required — acid environments containing oxidising impurities, chloride solutions, sulphur compounds, flue gas desulphurisation, waste treatment, pulp bleaching. If the conditions are not fully known, the safe choice is C-276.
In practice the decision comes down to this question: is the acid pure, or does it contain oxidising ions? If it is purely reducing, B-3; otherwise, C-276.
The other members of the family
For an intermediate solution resistant to both conditions there is Hastelloy C-2000, and for predominantly oxidising environments Hastelloy C-22.
Technical datasheets
Hastelloy B-3 — chemical composition, mechanical values, standard equivalents
Hastelloy C-276 — 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.