Environment Effects on Chromia (Cr2O3) Scale Stability Formed on Type 310S Stainless Steel During Wet Oxidation

The possibility of surrogating high-pressure supercritical water (SCW) with an ambient pressure air-10% H2O (wet air) mixture for studying wet oxidation of Type 310S stainless steel (UNS S31008) at high temperatures was examined using gravimetric measurements coupled with electron microscopy techniques. A distinctly different wet oxidation kinetic rate law was observed in the two environments at 550°C: parabolic for the wet air mixture and para-linear (“breakaway”) for SCW. The differing rate law is attributed to differences in the mass transport kinetics parameters, which are not well defined for SCW, that likely control Cr volatilization from the oxide scale, starting with the presumed MnCr2O4 spinel outer layer. Although the wet air mixture is not considered to be a suitable surrogate environment for SCW at the temperature of interest, it may prove useful to help determine microstructure instability effects on wet oxidation at elevated temperatures.