Characterisation of the austenitic steels Super 304H and HR3C after air and steam oxidation

This work aimed to evaluate the effect of a long-term pre-oxidation process in the air (5000 hours at 650 degrees C) on the steam oxidation resistance of Cr-rich steels with around 18 wt.% Cr (Super 304H) and around 25 wt.% Cr (HR3C) content exposed for the additional 5000 hours at 650 degrees C. The effect showed a high impact of a long-term pre-oxidation process and a high content of Cr in the metal matrix of the exposed steels. The steel with a lower Cr content showed spallation of the oxide scale under the oxidation process in the air, and only the steel with 25 wt.% Cr showed no spallation of the oxide scale in both conditions: air and steam. The post-exposure analysis in this work was carried out using Scanning Electron Microscopy (SEM) supported by Energy Dispersive X-ray Spectroscopy (EDS) using an X-Ray mapping function. Phase analysis was performed using an XRD diffractometer.