Corrosion Behaviour of High-Carbon High-Molybdenum Stellite Alloys in Amine Environment

Stellite alloys are cobalt-based alloys which display exceptional mechanical properties, wear and corrosion resistance owing to its unique chemical compositions. Stellite 6, which is used for hardfacing of valve trim components within control valves in boiler feedwater systems, have failed in application where hydrazine and amine derivatives are used. To find a better replacement of Stellite 6 for improved corrosion resistance, 700 series Stellite alloys, including Stellite 706, Stellite 712 and Stellite 720, are proposed, which are high-carbon high-molybdenum Stellite alloys. The corrosion performance of these alloys is studied using various testing methods in morpholine solution with pH 9.5. It is shown that these 700 series Stellite alloys are comparably better than Stellite 6 with respect to oxide film stability, general and localized corrosion resistance. The outcomes of this research suggest that 700 series Stellite alloys are good candidates for replacing Stellite 6.