Corrosion Performance of 700 Series Stellite Alloys in Various Media

Abstract

The corrosion performance of 700 series Stellite alloys including Stellite 706, Stellite 712 and Stellite 720, which are high-carbon high-molybdenum Stellite alloys, in various media such as Green Death solution, 3.5 wt.% NaCl solution and morpholine solution with pH 9.5, is studied using electrochemical and immersion methods. The obtained polarization curves are analyzed along with the corroded surfaces examined using SEM/EDS to investigate the corrosion mechanisms of these alloys. The experimental results reveal that the 700 series Stellite alloys possess excellent corrosion resistance in the tested media, even in the severe corrosive condition—Green Death solution at 60 °C where no noticeable pitting is found on the surfaces of the alloys. It is shown that the corrosion resistance of these Stellite alloys depends strongly on the behavior of the passivation film formed on the alloy surfaces. Additional Mo content in these alloys benefits the stabilization of the passivation film thus enhances the corrosion resistance of the alloys. Both carbon and molybdenum contents affect the passivation film formation and stabilization.