Corrosion of chromium containing alloys in non-steady state environments containing oxygen, carbon, and chlorine

Internal attack of chromium containing alloys in mixed oxygen-chlorine environments occurs by the formation of pores which penetrate down grain boundaries of the alloys. No internal attack was detected in a binary Fe-20 %Cr alloy at 1200 K in environments containing 2500 ppm C12. The rate of internal attack of alloy 800H in such environments was increased by replacing the O2 in the gas by C02 . In mixed oxygen-carbon-chlorine environments, the internal attack occurs by selective chlorination of chromium carbides which precipitate along the grain boundaries.