Influence of temperature and strain rate on the deformation and damage mechanisms of oxide dispersion strengthened ferritic steels

Deformation and damage mechanisms of Fe-14Cr based oxide dispersion strengthened (ODS) steels have been investigated through a multi scale approach on model materials elaborated by powder metallurgy Uniaxial tensile behavior was studied from room temperature to 800 degrees C at several strain rates. Furthermore, the plasticity of Fe-14Cr ODS steels has been analyzed at the grain scale by in situ transmission electron microscopy (TEM) straining experiments between room temperature and 650 degrees C, evidencing a clear evolution with temperature of the dislocation motion. The evolution of yield stress with temperature has been separated into three domains, which can be explained by changes of deformation mechanisms. At low temperatures, the hardening is associated to the pining of dislocations on nano-oxides whereas dislocations motion is thermally activated at higher temperatures. M high temperatures, a competition between intra- and inter-granular mechanisms is observed. The transition in damage mechanism, related to the change of deformation mode, explains the observed reduction of ductility.