HASTELLOY C-276 Properties

Engineering variability

• Cold work raises strength because the alloy is not precipitation hardened by conventional heat treatment.
• Thermal conductivity is low and rises with temperature.
• High-temperature service must consider phase stability and oxidation as well as strength.
• Corrosion resistance depends on chemical species, concentration, temperature, aeration and weld condition.

Selection note

Strong candidate for aggressive chemical-processing, pollution-control and sour/corrosive environments where stainless steel or less-alloyed nickel grades are insufficient.

Where a property is shown as qualitative rather than numeric, that is intentional: the selected source or the material physics does not justify a single comparable scalar.

Where it is specified

C-276 goes into chemical process equipment handling hot chlorides, wet chlorine, hypochlorite, sulphuric and hydrochloric acid mixtures; flue-gas desulphurisation scrubbers and stack liners; pulp and paper bleaching plant; pharmaceutical reactors; and waste incineration gas cleaning.

Its distinguishing quality is breadth. High molybdenum (about 16%) gives resistance to reducing acids, while chromium (about 15%) covers oxidising conditions — so it performs where a process stream is variable, contaminated, or upset in ways a more specialised alloy would not survive.

Chosen over what

Against 316L: an order of magnitude more expensive, specified only where stainless has failed or is known to be inadequate. The cost is justified by avoided downtime, not by material performance alone.

Against Inconel 625: better in reducing acids and in mixed contaminated streams; 625 is better in strongly oxidising service and at high temperature.

Against titanium: titanium excels in oxidising chlorides and seawater and is lighter, but is attacked by reducing acids and by dry chlorine. C-276 handles both oxidising and reducing conditions, which is why it is favoured when the stream changes.

Against glass-lined or PTFE-lined steel: C-276 tolerates thermal shock and mechanical damage that would destroy a lining, and can be welded and repaired in place.

How it fails

Intergranular attack after thermal exposure. The alloy's low carbon and tungsten content give it good as-welded corrosion resistance, but prolonged exposure in the 600–1000 °C range precipitates mu and P phases at grain boundaries and can sensitise it.

Crevice corrosion in hot, concentrated halide solutions — C-276 raises the threshold substantially but does not remove it.

Hot cracking during welding from segregation, particularly with high restraint or contaminated surfaces.

Erosion-corrosion in slurry service, where mechanical removal of the passive film outpaces repassivation.

Fabrication notes

Machinability is poor, comparable to 625 at roughly 15% of B1112, with severe work hardening. The practical rules are the same: rigid setup, sharp positive-rake tooling, constant heavy feed, flood coolant, and never let the tool rub.

Weldability is good and the alloy is normally used in the as-welded condition without post-weld heat treatment — the principal reason it is preferred for site-fabricated and repaired equipment. Matching ERNiCrMo-4 filler is standard.

Heat input must be kept low with controlled interpass temperature to avoid precipitation, and surfaces must be scrupulously clean, since sulphur and other low-melting contaminants cause hot cracking.

Cold forming is possible but the alloy work-hardens rapidly; intermediate solution annealing is often required for deep-drawn shapes.