Nickel based alloy are one of the essential classes of engineering materials that are widely used in the various environments and applications. These materials are chosen for aqueous and high temperature corrosion resistance applications. Nickel base alloys are used at cryogenic temperatures and reaching 1200oC because the matrix of solid solution alloys remains austenitic from solidification to absolute zero. Variety of these alloys are found for their ability of nickel matrix to alloy with large magnitudes of elements like chromium, iron, molybdenum and more while retaining essentially a single phase centered cubic structure.

Nickel based alloys are usually used in higher proportion of their melting point as compare to any other group of engineering materials for their supreme creep, fatigue and oxidation resistance. Nickel based alloys are mainly intended to meet the needs of wide range of applications in aircraft, power plant production, petrochemical, defense and transport industry. As different applications involve welding as a fabrication step, it is essential achieve good quality welding joints that can function adequately when used in similar strenuous service and environmental conditions as of the base metal.

Selection of Hastelloy C276

Hastelloy C276 is a highly corrosion resistant nickel based superalloy that finds applications in varied process industries. It offers outstanding resistance to corrosion in different conditions occurred during chemical processing and allied industries. The alloy is highly resistant to oxidizing and reducing conditions and is also a suitable material for use in naval and marine conditions. Evaluation for crevice corrosion in stagnant and running seawater showed that Hastelloy C276 does not attain crevice corrosion. Critical crevice and pitting temperatures in tests performed as per ASTM G48 methods C & D stated the higher resistance of alloy to crevice and pitting corrosion as compared to stainless steel 304SS, Incoloy 825 and Inconel 625.

It is a single phase super alloy with main alloying elements are chromium, molybdenum, iron and tungsten. Hastelloy C276 is designed for solid solution strengthening, without precipitation hardening operation. Chromium allows development of passive layers in different oxygen based conditions, hence adding to enhancement of corrosion resistance. Chromium also contributes to solid solution reinforcement. Molybdenum resists corrosion in reducing conditions and also offers significant strength to the FCC solid solution due to its atomic size. The elements chromium, iron and molybdenum are commonly used as solid solution strengtheners. Elements that attain similar atomic radii, electron radii, electronic structure and crystal structure relative to nickel are usually likely to remain in solid solution. Due to its larger atomic size as compared nickel, chromium offers strong solid solution strengthening effect. Molybdenum and tungsten provide an excellent combination of atomic radii mismatch and significant solubility required for solid solution reinforcement. These elements participate in solid state precipitation reactions and are used in high temperature operations. Hastelloy C276 is a highly corrosion resistant material and is widely used in FGD conditions that are the most aggressive conditions in the chemical industrial sector.