Atomic probe tomography study of the effect of thermal aging on the nanostructure of oxide dispersion-strengthened steels

In the present work, the effect of thermal aging on the nanostructure of three oxide dispersion-strengthened steels with different alloying systems: Eurofer ODS, 10Cr ODS and KP-3 ODS was investigated by atom probe tomography. The investigated steels were aged at 650°C for 500 and 1000 h. Nanoscale clusters enriched in Y, O and Cr, as well as in V, Ti and Al depending on the alloying system of the steel were found in all states. Investigation of the changes in the nanostructure of steels after thermal aging for 500 h showed a significant increase in the number density of clusters in all steels, while after 1000 h aging their number density decreased in Eurofer ODS and 10Cr ODS, or remained at the same level in KP-3 ODS. At 500 h, the retention (10Cr ODS, KP-3 ODS) or increase (Eurofer ODS) of the average cluster size was also observed, while at 1000 h the average size was stable in Eurofer ODS and 10Cr ODS, or experienced a slight decrease in KP-3 ODS. Analysis of the nanostructure change showed first an increase in the number density of clusters (while maintaining or increasing the average size) in all steels during aging up to 500 h, corresponding to the nucleation stage of new clusters. After aging for 1000 h, a decrease in number density was found, corresponding to the maturation stage. These tendencies are also confirmed by analyzing the changes in the concentration of chemical elements in the matrix.