Residual stress analysis in thermally grown oxide scales developed on Nb-alloyed refractory austenitic stainless steels

Abstract

Abstract Reliable high temperature operation of refractory metals depends on the mechanical integrity of the protective oxide formed on the material surface. The residual stress state in oxide layers developed on two modified Nb-alloyed ASTM A297 HH austenitic stainless steels, thermal expansion analysis of the substrate, steel microstructure, oxide layers morphology and phases composition were analyzed. The experimental analyses revealed that larger Nb additions increased NbC precipitates, which was connected to lower thermal expansion coefficient of the substrate. Despite similarities in the oxide scales, the higher Nb-alloyed samples exhibited lower magnitude residual stress values and larger spallation after long-term oxidation.