The effect of hydrogen on a transition of internal/external oxidation in high temperature oxidation of Fe-Cr alloy at 1073 K

摘要

Steam is frequently detrimental to an oxidation resistance of high temperature alloys. Hydrogen, which is dissociated from steam, shall play important roles. Wagner proposed a formula to represent a transition of internal/external oxidation in high temperature alloy. Considering a Fe-Cr alloy, the transition depends on a diffusivity of Cr and a permeability of O in the alloy. The diffusivities of Cr were obtained from concentration profiles of Fe/Fe-16mass%Cr diffusion couples annealed at 1073 K in vacuum or under Ar-20%H_2 flows. The permeability of O was obtained by internal oxidation technique using Fe-5Cr. The hydrogen has ignorable effect on diffusivity of Cr in Fe-Cr alloy but increase the permeability of O in alloy. The increase in the oxygen permeability requires the higher Cr concentration to form the external scale. It is considered that the change is one of the reasons for the detrimental effect of steam on the oxidation of the alloy.