About the role of chromium and oxygen ion diffusion on the growth mechanism of oxidation films of the AISI 304 austenitic stainless steel.

Abstract

To study the role of ion diffusion on the oxidation process of the AISI 304 austenitic stainless steel, chromium diffusion coefficients were determined in oxide films grown on this steel at 750, 800 and 850 C, in air. The isotope 54Cr was used as a chromium tracer and the diffusion profiles were established by SIMS. The bulk diffusion coefficients are five orders of magnitude smaller than the grain boundary diffusion coefficients. It was found that the values of the chromium diffusivities are lower than the corresponding oxygen diffusivities obtained in previous work. Parabolic oxidation constants calculated as a function of the chrome and oxygen diffusivities, using Wagner0 s theory, are close to those determined experimentally, which shows that the growth rate of chromia is controlled by ion diffusion, but inward oxygen diffusion plays the main role on the growth kinetics of chromia formed by the oxidation of the AISI 304 steel.