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.

Automated summary

The long-term pre-oxidation process and high Cr content have a significant impact on the oxidation resistance of the steel. The steel with lower Cr content showed spallation of the oxide scale, whereas only the steel with higher Cr content exhibited no spallation in both air and steam conditions.