Preparation and characterization of nano-structured 14Cr-ODS ferritic steel

Nano-structured oxide dispersion strengthened (ODS) ferritic steels are the leading candidates of fuel cladding for future fast neutron feeder reactors due to their excellent radiation tolerance and high-temperature creep strength. A 14Cr-ODS steel was prepared by mechanical alloy (MA) and hot isostatic pressing (HIP) methods. The morphology and microstructure of MA powders and the microstructure of 14Cr-ODS steel were characterized by SEM, XRD, EDS and TEM. The results showed that during the MA, the size of powders increases with the increasing milling time (0-2 h), then decreases with the increasing milling time (2-70 h). The grain size decreases with the increasing milling time. The alloying elements and Y ₂O ₃ dissolve fully into Fe matrix during MA after 70 h. Three kinds of precipitates are observed in the consolidated 14Cr-ODS steel: very high number density of nanoscale Y-Ti-O-rich clusters, few pyrochlore structure Y ₂Ti ₂O ₇ particles and some Cr-Ti-rich particles. The clusters exhibits good high temperature stability at 1250°C for 8 h, while the density of Y ₂Ti ₂O ₇ precipitates increases.