Annealing Effects on the Microstructure of Ferritic-Martensitic ODS-Eurofer Steel

Oxide dispersion strengthened (ODS) ferritic/martensitic (FM) steels are promising candidates for structural applications in future fusion power reactors. In order to evaluate the thermal stability of 80% cold-rolled ODS-EUROFER, samples were annealed for 1 h at temperatures up to about 0.9 T_m, where T_m is the absolute melting point. The characterization of the annealed samples was performed using transmission electron microscopy and electron backscatter diffraction. Results show that static recovery is the main softening mechanism of this steel when annealed below 800°C. The volume fraction of recrystallized grains is quite small (below 0.10). Above 900°C, martensitic transformation takes place causing pronounced hardening. Large M₂₃C₆ particles are found at the grain boundaries after tempering at 750°C for 2 h.