C276 Superalloy
Hastelloy C276 (often referred to simply as C276) is a nickel-molybdenum-chromium superalloy celebrated for its exceptional corrosion resistance in extreme environments, including high temperatures, acidic solutions, and oxidizing/reducing conditions. Unlike some high-temperature superalloys focused primarily on strength at elevated temperatures, C276 balances heat resistance with unparalleled chemical durability, making it a cornerstone material in chemical processing, energy, and marine engineering.
Basic Information
Definition: C276 is a solid-solution-strengthened nickel-based alloy, meaning its strength comes from the uniform distribution of alloying elements in the nickel matrix rather than precipitation hardening. This structure grants it excellent ductility and weldability while maintaining stability at high temperatures.
Corresponding Standards: Complies with international specifications such as ASTM B575 (wrought products), ASTM B574 (bars), and ASME SB-575. It is designated as UNS N10276 and Werkstoff Nr. 2.4819.
Key Characteristics: Superior corrosion resistance (especially to pitting, crevice corrosion, and stress corrosion cracking), good high-temperature strength up to 1093°C (2000°F), and excellent weldability without post-weld heat treatment.
Chemical Composition
C276’s composition is meticulously engineered to resist a wide range of corrosive media, with molybdenum and chromium as core alloying elements:
Element Content Range Role in the Alloy
Nickel (Ni) 余量 (Balance) Base element; provides a stable austenitic matrix and supports corrosion resistance.
Molybdenum (Mo) 15.0–17.0% Enhances resistance to pitting, crevice corrosion, and reducing acids (e.g., hydrochloric acid).
Chromium (Cr) 14.0–16.0% Improves oxidation resistance and performance in oxidizing environments (e.g., nitric acid).
Iron (Fe) 4.0–7.0% Enhances ductility and fabricability while reducing material cost.
Tungsten (W) 3.0–4.5% Boosts strength and corrosion resistance, particularly in high-temperature applications.
Cobalt (Co) ≤2.5% Controlled to minimize sensitivity to certain corrosive environments.
Carbon (C) ≤0.01% Strictly limited to prevent carbide formation, which can reduce corrosion resistance in welded areas.
Silicon (Si) ≤0.08% Minimized to avoid forming brittle intermetallic phases and reduce oxidation issues.
Manganese (Mn) ≤1.0% Aids in deoxidation during processing; controlled to avoid impairing corrosion resistance.
Phosphorus (P) ≤0.04% Limited to prevent grain boundary brittleness.
Sulfur (S) ≤0.03% Minimized to avoid hot cracking during welding.
Physical Properties
Density: Approximately 8.89 g/cm³.
Melting Point: 1325–1370°C (2417–2500°F).
Thermal Conductivity: ~10.8 W/(m·K) at 20°C; increases to ~19 W/(m·K) at 650°C.
Coefficient of Thermal Expansion: ~12.3×10⁻⁶/°C (20–100°C); ~15.2×10⁻⁶/°C (20–650°C).
Elastic Modulus: ~205 GPa at 20°C; ~186 GPa at 650°C.
Magnetic Properties: Non-magnetic in all conditions.
Mechanical Properties
C276 exhibits reliable strength at both ambient and elevated temperatures, with a focus on ductility and toughness:
Typical Properties (Annealed Condition)
Property Value (Room Temperature) Value (650°C)
Tensile Strength ≥690 MPa ≥550 MPa
Yield Strength (0.2% offset) ≥280 MPa ≥240 MPa
Elongation ≥40% ≥45%
Hardness ~90–100 HRB ~85 HRB
Creep Resistance: Adequate for moderate high-temperature applications (e.g., <0.5% creep strain after 1000 hours at 650°C under 140 MPa stress). Impact Toughness: Excellent—~120 J (Charpy V-notch) at room temperature; retains toughness at cryogenic temperatures. Fatigue Strength: ~240 MPa (10⁷ cycles at room temperature), suitable for cyclic load applications in corrosive environments. Heat Treatment C276 does not require precipitation hardening and is typically used in the annealed condition to optimize corrosion resistance and ductility: Annealing Process: Temperature: 1120–1175°C (2050–2150°F), held for 30–60 minutes. Cooling: Rapid air cooling or water quenching to prevent carbide precipitation at grain boundaries, which could impair corrosion resistance. No Post-Weld Heat Treatment: Unlike many superalloys, C276 welded joints retain corrosion resistance without additional heat treatment, simplifying fabrication. Processing Performance Weldability: Excellent—can be welded using GTAW (TIG), GMAW (MIG), and submerged arc welding. Low carbon content minimizes carbide formation in the heat-affected zone (HAZ), preserving corrosion resistance. Machinability: Moderately challenging due to work-hardening tendencies. Requires sharp carbide tools, low cutting speeds, and copious coolant to prevent tool wear and maintain surface integrity. Forming: Cold forming is feasible with adequate ductility, though heavy deformation may require intermediate annealing to restore workability. Hot forming is possible at 980–1120°C (1800–2050°F). Application Fields C276’s primary strength lies in its corrosion resistance across extreme environments, making it indispensable in industries where chemical attack is a critical concern: Chemical Processing: Reactors, heat exchangers, and piping for handling acids (sulfuric, hydrochloric, acetic), chlorinated solvents, and chemical intermediates. Components in pharmaceutical and fine chemical production where purity and corrosion resistance are paramount. Energy Industry: Flue gas desulfurization (FGD) systems in power plants to resist acidic byproducts. Oil and gas offshore platforms, downhole tools, and subsea pipelines exposed to brines and corrosive hydrocarbons. Marine Engineering: Propeller shafts, seawater intake systems, and hull components for ships and offshore structures, resisting saltwater corrosion and biofouling. Environmental Technology: Waste incineration equipment and pollution control systems handling corrosive exhaust gases. Aerospace & Defense: Exhaust systems and engine components in marine gas turbines, where high temperatures and salt exposure are prevalent. In summary, Hastelloy C276 stands out as a "workhorse" superalloy for corrosive environments, offering a rare combination of chemical resistance, high-temperature stability, and fabricability. Its ability to perform reliably in harsh conditions has made it a trusted material in industries where failure due to corrosion is unacceptable.