What Is C-276 Alloy (UNS N10276)?
C-276 is a low-carbon nickel-chromium-molybdenum alloy with tungsten additions, designated UNS N10276. It was developed to eliminate the intergranular corrosion that attacked earlier high-molybdenum grades: carbon and silicon are held at very low levels so that no continuous grain-boundary precipitate forms in the weld heat-affected zone. The result is an alloy that stays corrosion resistant in both the welded and the solution-annealed condition.
Its main strength is breadth. C-276 resists wet chlorine, oxidizing chlorides, chloride salt solutions, sulfuric acid and oxidizing salts, and it also performs well in low and medium temperature hydrochloric acid. For that reason it has been used for decades in chemical processing, petrochemical plants, flue gas desulfurization, pulp and paper mills and environmental protection equipment.
One trade-off should be noted: thermal stability is moderate. Long exposure above roughly 700 °C can promote precipitation, so high-temperature service is normally limited and the alloy is selected for its aqueous corrosion resistance rather than for creep strength.
Chemical Composition of C-276 Alloy
| Element | Composition, % | Element | Composition, % |
|---|---|---|---|
| Ni | Balance | Mo | 15.0–17.0 |
| Cr | 14.5–16.5 | W | 3.0–4.5 |
| Fe | 4.0–7.0 | Mn | 1.00 max |
| Si | 0.08 max | C | 0.02 max |
| P | 0.040 max | S | 0.03 max |
| V | 0.35 max | – | – |
Equivalent Designations and Physical Properties
| System | Designation |
|---|---|
| UNS | N10276 |
| DIN / EN | 2.4819 |
| GB | NS3304 (former 00Cr16Ni60Mo16W4) |
| Physical property | Value | Condition |
|---|---|---|
| Density | 8.885 g/cm³ | Room temperature |
| Thermal conductivity | 9.4–28 W/(m·K) | 100–1092 °C |
| Electrical resistivity | 1.30 µΩ·m (1.30 Ω·mm²/m) | Room temperature |
| Specific heat capacity | 427 J/(kg·K) | Room temperature |
| Linear expansion coefficient | 14.1 × 10⁻ /K | 20–649 °C |
Mechanical Properties After Cold Reduction
Cold work raises the strength of C-276 plate sharply while ductility falls. The table below shows measured values for 2.4 mm plate tested at room temperature after different cold reductions.
| Cold reduction | Tensile strength, MPa | Elongation, % |
|---|---|---|
| 0 % (solution annealed) | 806 | 67 |
| 10 % | 894 | 48 |
| 20 % | 1021 | 26 |
| 40 % | 1336 | 9 |
Because of this work-hardening response, cold forming is scheduled to finish near the final size, and intermediate anneals are used when a large reduction is unavoidable. The solution-annealed condition gives the best combination of ductility and corrosion resistance.
Processing, Welding and Heat Treatment
Hot working is difficult because the alloy deforms only in a narrow window; the recommended range is 1000–1200 °C with a finishing temperature high enough to avoid cracking. Cold working performance is good in the solution-annealed state. Heat treatment is carried out at approximately 1220 °C followed by rapid water quenching, which keeps alloying elements in solution and restores corrosion resistance after welding or forming.
Welding is easier than with the earlier C-grade alloys. Low heat input, matching nickel-base filler metal and clean joint faces are the key controls, and the surface oxide produced by welding must be ground or pickled away because it is cathodic to the base metal. Interpass temperature should be kept below about 150 °C, and no preheat is necessary. Machining is done with carbide tooling at low speed and heavy feed to stay ahead of the work-hardened layer.
Frequently Asked Questions
Q: What is C-276 alloy used for?
It is used for equipment handling strong media such as wet chlorine, oxidizing chlorides, chloride salt solutions, organic acids and halogen gases, including wet phosphoric acid plants, hydrofluoric acid production and flue gas desulfurization systems.
Q: What does UNS N10276 mean?
UNS N10276 is the unified numbering system designation for the low-carbon nickel-chromium-molybdenum-tungsten alloy known commercially as C-276.
Q: How does C-276 differ from C-22?
C-276 contains tungsten with molybdenum at 15.0–17.0 %, giving excellent resistance in reducing acids, while C-22 carries more chromium and is stronger in oxidizing media.
Q: Can C-276 be welded without intergranular corrosion?
Yes. Because carbon and silicon are kept very low, the alloy resists grain-boundary precipitation, so welded joints have no sensitisation zone of the type found in the older C-grade alloys.
Q: What is the solution annealing temperature for C-276?
Heat treatment is performed at about 1220 °C, followed by rapid water quenching to retain the alloying elements in solid solution.
Q: Which standards cover C-276 plate and pipe?
Plate, sheet and strip are specified by ASTM B575, seamless pipe and tube by ASTM B622, and welded pipe and tube by ASTM B619 and ASTM B626.
