The Effect of Water Vapor on the Transition from Internal to External Oxidation of Austenitic Steels at 1,073 K

Abstract

The effect of water vapor on the transition from internal to external oxidation of austenitic alloys has been conducted at 1,073 K under the equilibrium oxygen partial pressure for the coexistence of Fe and FeO. Critical Cr concentrations in the Fe–Cr–30Ni (at.%) austenitic alloys were determined to be 30 at.% in dry atmosphere and 37 at.% in humid atmosphere. Thus, water vapor significantly affected the transition from internal to external oxidation of austenitic alloys. Two oxides of Cr2O3 and FeCr2O4 precipitated in the Fe–5Cr–30Ni (at.%) alloy and solid state reaction for the formation of FeCr2O4 may be influenced by water vapor. Oxygen permeability, which was estimated by considering the effective stoichiometric ratio, was also enhanced by water vapor.