What Is nickel-molybdenum-chromium alloy UNS N10276?
nickel-molybdenum-chromium alloy UNS N10276, UNS N10276, is a tungsten-bearing nickel-chromium-molybdenum alloy with extremely low carbon and silicon contents, developed to survive the most aggressive chemical environments. It is known by several national designations: the German material number 2.4819 with designation NiMo16Cr15W, the French NC17D, and the Chinese grade NS334. The low carbon content minimizes carbide precipitation during welding, preserving resistance to intergranular corrosion in the heat-affected zone, and the low silicon content reduces stress and segregation issues during fabrication. C-276 is ductile, easy to form and weld, and offers excellent resistance to stress corrosion cracking in chloride-containing solutions, where austenitic stainless steel is prone to failure. Its combination of chromium and molybdenum resists both oxidizing and non-oxidizing acids and gives outstanding resistance to pitting and crevice corrosion in chloride and other halide environments.
Chemical Composition
The composition of C-276 is tightly controlled to balance corrosion resistance with fabricability. Per ASTM B575 for plate, sheet, and strip, the limits are nickel as balance, molybdenum 15.00-17.00%, chromium 14.50-16.50%, iron 4.00-7.00%, tungsten 3.00-4.50%, cobalt 2.50% maximum, manganese 1.00% maximum, silicon 0.08% maximum, vanadium 0.35% maximum, carbon 0.01% maximum, phosphorus 0.040% maximum, and sulfur 0.030% maximum. Molybdenum and tungsten provide resistance to reducing acids and localized chloride attack, chromium supplies oxidizing resistance, and the very low carbon and silicon protect weldability and intergranular corrosion resistance.
Physical and Mechanical Properties
| Property | Value |
| Density | 8.89 g/cm3 |
| Melting range | 1325-1350°C |
| Tensile strength (annealed, min per ASTM B575) | 690 MPa (100 ksi) |
| Yield strength (annealed, min) | 283 MPa (41 ksi) |
| Elongation (min) | 40% |
| Hardness (annealed) | About 90 HRB typical |
The values above follow ASTM B575 for the annealed condition. In the solution-treated state, C-276 offers the best combination of corrosion resistance and mechanical properties, with good toughness from cryogenic temperatures up to its practical service limit. Design values should always be taken from the governing code and the certified mill test report.
Heat Treatment, Welding and Fabrication
Unless the application specifies otherwise, C-276 is supplied in the solution-annealed condition: heated to about 1121°C (2050°F) and then rapidly cooled, typically by water quenching. This state dissolves secondary phases and maximizes corrosion resistance and ductility. The alloy must not be exposed to the 650-1090°C range for extended periods during processing, because harmful phases such as mu phase can precipitate and reduce toughness and corrosion resistance. For the same reason, post-weld heat treatment is generally not required and should be avoided unless specifically mandated and carefully controlled.
C-276 welds readily by conventional processes, with TIG (GTAW), MIG (GMAW), and manual arc (SMAW) the most common, using matching filler such as ERNiCrMo-4. Oxy-acetylene welding is not recommended when corrosion resistance is required, and submerged arc welding needs particular care because its high heat input can promote phase precipitation and segregation in the weld. Control heat input and interpass temperature, keep joint surfaces clean, and use argon backing on the root pass for optimum weld quality. For hot working, C-276 is forged, rolled, pressed, extruded, or formed within a narrower temperature window than austenitic stainless steel, with a recommended initial forging temperature of about 1232°C and final forging temperature of about 954°C; moderate deformation with frequent reheats gives the best results. In cold forming the alloy is harder than most austenitic stainless steels and requires more energy, and the material work-hardens, so powerful equipment and, for severe deformation, intermediate annealing are needed.
Applications and Service Considerations
C-276 is used for chemical reactors, columns, heat exchangers, piping, and fittings handling wet chlorine, hypochlorite, sulfuric, hydrochloric, phosphoric, and acetic acids, and for flue gas desulfurization scrubbers, offshore seawater systems, and pollution control equipment. In continuous service the alloy is commonly rated up to about 650°C for structural duty, while corrosion service temperatures are usually lower and depend on the media; short excursions above this are possible but should be verified against the design code. Like all high-performance alloys, C-276 should be confirmed against the specific process chemistry, because severely oxidizing media such as hot nitric acid, or fluorides in some conditions, can attack even this alloy.
Frequently Asked Questions
What is nickel-molybdenum-chromium alloy UNS N10276? nickel-molybdenum-chromium alloy UNS N10276, UNS N10276, is a tungsten-bearing nickel-chromium-molybdenum alloy with very low carbon and silicon, resistant to oxidizing and reducing acids, chlorides, pitting, crevice corrosion, and stress corrosion cracking.
What is the composition of C-276? Nominally molybdenum 15.0-17.0%, chromium 14.5-16.5%, iron 4.0-7.0%, tungsten 3.0-4.5%, cobalt 2.5% maximum, carbon 0.01% maximum, silicon 0.08% maximum, with nickel as balance, per ASTM B575.
What is C-276 resistant to? It resists wet chlorine, hypochlorite, sulfuric, hydrochloric, phosphoric, and acetic acids, chloride pitting and crevice corrosion, and stress corrosion cracking in chloride solutions, making it a versatile choice for chemical and pollution control service.
Can C-276 be welded? Yes. TIG, MIG, and manual arc welding with ERNiCrMo-4 filler are standard, with controlled heat input and clean surfaces. Oxy-acetylene welding should not be used where corrosion resistance matters, and submerged arc welding needs special heat-input control.
What is the maximum service temperature of C-276? For structural service the alloy is commonly rated to about 650°C (1200°F) in continuous use, with the exact limit depending on the code and application. Corrosion service temperatures are usually lower and set by the process chemistry.
Which standards cover nickel-molybdenum-chromium alloy UNS N10276? ASTM B575 for plate, sheet, and strip; B574 for rod and bar; B622 for seamless pipe; B619 and B626 for welded pipe; B366 for fittings; and B564 for forgings, with ASME SB equivalents for pressure equipment.
Is C-276 magnetic? In the solution-annealed condition the alloy is essentially non-magnetic, as expected for an austenitic nickel-base alloy, and it remains non-magnetic after welding and typical service.
