CORROSION MECHANISMS OF HIGH CHROMIUM ALLOYS IN CARBURIZING ENVIRONMENTS.

High chromium alloys used in high temperature service are susceptible to carburization in high carbon activity environments. This form of corrosion leads to the precipitation of chromium rich carbide phases M//2//3C//6 and M//7C//3 in the alloy interior with resultant degradation of the high temperature mechanical properties of the alloy. One approach to limit carburization is to control the environmental parameters such that a passivating Cr//2O//3 layer can form on the alloy surface. Another approach, especially under conditions where CrO is unstable, is to use an inhibitor such as sulfur. In the present work, the kinetics of carburization of model Fe-Cr and Ni-Cr alloy systems are investigated in purely carburizing H//2-Ch//4 gas mixtures in which Cr//2O//3 scales are essentially unstable. The influence of sulfur in inhibiting carburization is investigated.