Alloy C-276 (UNS N10276) Corrosion-Resistant Bar: Properties and Applications
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Alloy C-276, UNS N10276, is a nickel-molybdenum-chromium alloy with a tungsten addition, developed for severe corrosive service where stainless steels and lower-alloy nickel grades fail. Bar stock in this grade is held for chemical processing, pollution control, marine and offshore duty, and for components such as valve stems, pump shafts, fasteners and agitator shafts that must keep their strength while resisting both oxidising and reducing media.
What Alloy C-276 Is
The alloy is balanced around a high nickel content that provides a stable, ductile austenitic matrix, molybdenum that gives resistance to reducing acids such as hydrochloric and sulfuric acid, and chromium that protects against oxidising conditions and hot oxidising gases. Tungsten further improves resistance to pitting and crevice attack.
The low carbon and silicon levels limit carbide and intermetallic precipitation during welding, so the corrosion resistance of the weld heat-affected zone stays close to that of the parent bar and post-weld heat treatment is not required in most applications. The corresponding European designations are NiMo16Cr15W and material number 2.4819.
Chemical Composition of Alloy C-276 Bar
| Element | Composition, % |
|---|---|
| Nickel (Ni) | Balance |
| Molybdenum (Mo) | 15.0 - 17.0 |
| Chromium (Cr) | 14.5 - 16.5 |
| Iron (Fe) | 4.0 - 7.0 |
| Tungsten (W) | 3.0 - 4.5 |
| Cobalt (Co) | 2.5 max |
| Manganese (Mn) | 1.0 max |
| Carbon (C) | 0.010 max |
| Silicon (Si) | 0.08 max |
| Phosphorus (P) | 0.040 max |
| Sulfur (S) | 0.030 max |
These limits follow the requirements for UNS N10276 in ASTM B574 / ASME SB574, the specification covering nickel alloy rod and bar. The carbon and silicon ceilings are the reason the grade is selected for welded equipment, because they suppress the grain-boundary precipitation that would otherwise reduce corrosion resistance next to a weld.
Mechanical and Physical Properties
| Property | Typical value, annealed bar |
|---|---|
| Tensile strength | 785 MPa or higher |
| Yield strength, 0.2% offset | 355 MPa or higher |
| Elongation | 40% or higher |
| Hardness | 95 HRB maximum |
| Density | 8.89 g/cm3 |
| Melting range | about 1325 - 1370 C |
Mechanical property requirements for rod and bar are stated in ASTM B574 / ASME SB574; the values above describe the annealed condition normally stocked, and cold-worked bar is available when higher strength is needed. The alloy keeps useful strength at elevated temperature and remains ductile at sub-zero temperatures, which is why it also appears in cryogenic and sour-service equipment.
Product Forms, Sizes and Packing
Round bar from 6 mm to 100 mm diameter, plus flat bar, square bar, hexagon bar and forging stock
Lengths cut to order, typically 3 m, 4 m or 6 m random lengths, with sawn or peeled ends
Condition: hot worked and annealed, or cold drawn, turned, ground or polished for close-tolerance machining
Each bar wrapped in anti-rust paper and waterproof film, packed in wooden boxes or on steel pallets
Marking shows heat number, grade, condition and size so that the bar can be traced to its test certificate
Applications and Corrosion Performance
The grade is used for chemical process equipment such as reactors, heat exchangers, scrubbers and columns; for marine and offshore platform piping and fittings; for flue-gas desulphurisation and other pollution control systems; for pharmaceutical and pulp and paper plant components; and for acid production, pickling and acid handling equipment.
Because it resists both oxidising and reducing media, the alloy tolerates environments that attack stainless steel, including chlorides, hypochlorite, wet chlorine and mixed acids, and it resists pitting and crevice corrosion in seawater. For sour oil and gas service the material is commonly qualified to NACE MR0175 / ISO 15156 and supplied with hardness and chemistry verification. Where high-temperature strength rather than corrosion resistance is the design driver, the same product form is available to ASTM B564 for forgings, B575 for plate, sheet and strip, B622 for seamless pipe and tube, and B619 or B626 for welded pipe and tube, so a complete fabrication can be ordered to one alloy family.
Frequently Asked Questions
Q: What is Alloy C-276 used for?
It is used for components in severe corrosive service, including reactors, heat exchangers, scrubbers, marine and offshore piping, pollution control equipment, pickling lines and pharmaceutical plant items.
Q: Does Alloy C-276 need post-weld heat treatment?
Generally no. Low carbon and silicon contents limit precipitation in the heat-affected zone, so welds retain corrosion resistance without a post-weld anneal in most chemical and marine applications.
Q: How does C-276 compare with stainless steel?
Stainless steel relies on a chromium-rich passive film and suffers in chloride or strongly reducing acid service, while the high molybdenum and tungsten content of C-276 gives it much wider resistance to pitting, crevice attack and reducing acids.
Q: What is the difference between UNS N10276 and the other members of the same alloy family?
N10276 is the original low-carbon, low-silicon grade with broad resistance to both oxidising and reducing media; higher-chromium or lower-molybdenum derivatives were developed for particular environments such as oxidising acids or alkaline service.
Q: Can C-276 bar be machined easily?
The alloy work-hardens quickly and has low thermal conductivity, so it is machined with sharp positive-rake tooling, heavy feeds, low cutting speeds and generous coolant flow to keep heat out of the cutting edge.
Q: Why is the alloy supplied with a heat number and test certificate?
Traceability is essential for pressure and chemical plant components, so each bar carries a heat number that links it to the chemical analysis, mechanical test and heat treatment records.
