HIGH-TEMPERATURE CORROSION OF MA 956 IN SULFIDIZING OXIDIZING CARBURIZING ENVIRONMENTS - A STUDY OF THE INFLUENCE OF PREOXIDATION ON THE CORROSION-RESISTANCE OF THE ALLOY

The influence of preoxidation and of the presence of HCl or of char de posits upon the high temperature corrosion of MA 956 in simulated coal -gasification environments has been studied at 700-degrees-C for perio ds up to 2000 h. The corrosion of the blank material produced mixed Al -Cr sulfide-oxide scales, while preoxidation led to the development of alumina scales well adherent to the substrate which were quite protec tive since no sulfide formation was observed even after 1000 h exposur e to the sulfidizing gases. On the contrary, HCl produced a significan t enhancement of the corrosion rate of the bare alloy: however, preoxi dation was able to afford a reasonable degree of protection even in th is case. Coal chars had little effect on the corrosion in the absence of HCl.