High temperature oxidation of austenitic stainless steel in low oxygen pressure

The oxidation of unstabilized austenitic stainless steel (En 58A) at temperatures between 770 to 1070 K in 10-5Nm-2 oxygen pressure is reported. The surface composition was determined during oxidation by Auger electron spectroscopy and measurements carried out when oxidation was complete were made using energy dispersive X-ray analysis and electron microprobe analysis. The influence on the subsequent oxidation characteristics of trace and minor elements present in the bulk alloy was found to be important. Initially the formation of surface oxide was retarded by the diffusion of sulphur from the bulk. Subsequently manganese diffused through the first formed oxide at a rate two orders of magnitude greater than chromium to form a major fraction of the surface oxide. Diffusion rates for sulphur through the bulk alloy and manganese and chromium through the oxide have been determined and a mechanism for the high temperature oxidation of unstabilized austenitic stainless steel in low oxygen pressures is proposed. (author)