Hastelloy C276 (UNS N10276): Where It Wins and How to Buy It

Quick answer: Hastelloy C276 (UNS N10276) is the default corrosion-resistant nickel alloy for the worst oxidizing-plus-reducing environments — hot, mixed-acid and chloride-pitting service where 316L, 904L and even Inconel 625 fall short. The trade-offs are price (roughly 4–7× 316L), poor machinability, and a narrow, non-negotiable solution-annealing window that must appear on the MTR.

What is Hastelloy C276 and where does it actually win?

C276 is a nickel–chromium–molybdenum alloy (16 Cr, 16 Mo, ~57 Ni) with tungsten added for solid-solution strengthening. Its strength is breadth: it resists pitting and crevice corrosion in hot chlorides, and it survives concentrated oxidizing acids (ferric/hydrochloric/nitric mixtures) that destroy stainless. The single most common use is flue-gas desulfurization, where flue gas, scrubber liquor and chlorides coexist at temperature — exactly the mixed environment that defeats single-mechanism alloys.

PREN is a guide, not a spec; C276's edge is reducing-acid resistance, not just the number.

Forms, standards and what to buy

• Bar: ASTM B574 (UNS N10276), commonly supplied in hot-finished, forged or cold-drawn condition; machined rounds up to large diameters.
• Plate and sheet: ASTM B575, with B564 forgings and B622/B619 seamless and welded pipe for the same alloy.
• Condition: C276 is supplied solution-annealed only. There is no age-hardening condition to specify — the heat treatment is what gives it corrosion resistance.

The solution-anneal line is the whole ballgame

C276 is a single-phase, solid-solution alloy. Its corrosion resistance comes entirely from a uniform, wrought-microstructure heat treatment — typically 1120–1170 °C followed by rapid quench. If the MTR does not show a completed solution-anneal (temperature, soak time, quench medium), do not accept the material: a cold-worked or improperly annealed C276 can corrode far below its rated performance. This is the one quality gate that separates good C276 from decorative C276.

Machining and welding cautions

• Machining: C276 work-hardens aggressively and has low thermal conductivity, so use rigid setups, low speeds, positive rake and flood coolant. Treat it like Inconel, not steel.
• Welding: It is weldable with matching N10276 filler or ERNiCrMo-4 wire, but the weld must not sensitize; keep interpass temperatures low and avoid re-heating the heat-affected zone. Post-weld heat treatment is not required and usually not wanted.
• Pickling: after welding, a proper pickling passivation restores the surface — relevant to the same surface-finish logic used on stainless pipe.

What should the C276 RFQ include?

1. Form and standard: bar per ASTM B574, plate per B575, etc.
2. Dimensions, tolerance class and whether machined surfaces are required.
3. Quantity, with the note that minimum melts make small orders expensive.
4. MTR requirement: solution-anneal parameters, chemistry per heat, UTS/elongation, and UT if the section is thick.
5. End use in one line — "RFQ: FGD scrubber nozzle, 90 °C, wet Cl⁻" tells the supplier which inspection depth to quote.

FAQ

Q: Is C276 better than Inconel 625? A: For mixed hot acid and pitting, yes — C276 has more molybdenum and tungsten and resists stronger oxidizers. For high-temperature strength and seawater fatigue, 625 is the better pick; the choice is driven by the dominant corrosion mechanism.

Q: Why is C276 so much more expensive than stainless? A: The molybdenum and tungsten content plus low, alloy-specific production volumes. On a whole-life basis it is often cheaper than replacing stainless equipment that corrodes out in months.

Q: Can C276 be used for seawater? A: It is excellent in seawater, but for pure seawater without acid many engineers use 625 or 6Mo (254SMO) at lower cost; reserve C276 for seawater that is also hot or chemically aggressive.

Q: How do I verify I got real C276? A: Positive material identification (PMI) for Ni/Cr/Mo/W, confirmed against the heat MTR, plus a check that the solution-anneal heat treatment is documented. PMI is cheap insurance on a 6×-cost material.