High temperature corrosion behaviour of iron aluminides and iron-aluminium-chromium alloys

The high temperature corrosion of different iron aluminides and iron-aluminium-chromium alloys containing between 6 and 17 wt% aluminium, 2 and 10 wt% chromium and additions of mischmetal has been investigated in air as well as in carburising, chlorinating and sulphidising environments. It was found that all alloys showed excellent corrosion resistance to both oxidation in air and carburisation in CH4/H-2 up to at least 1100 degrees C and to sulphidation in SO2/air up to at least 850 degrees C. In these environments the corrosion behaviour is not influenced by the concentrations of aluminium and chromium. In oxygen deficient H2S-atmospheres, however, the corrosion behaviour depends sensitively on the aluminium and chromium concentration. At least 12 wt% aluminium in chromium-free alloys or 10 wt% aluminium in alloys containing 10 wt% chromium are required to provide sulphidation resistance at 550 degrees C. The chlorination resistance of iron-aluminium-chromium alloys is low due to their formation of volatile aluminium chlorides.