Annealing effects on microstructure and coercive field of ferritic-martensitic ODS Eurofer steel

Research highlights: → ODS RAFM steels as structural material for fusion reactors. → Isothermal annealing of 80% deformed steel. → Recovery and recrystallization in the ferritic phase field. → Martensitic transformation takes place above 800 deg. C. → Microstructural changes during annealing are mirrored by coercive field measurements. - Abstract: Oxide dispersion strengthened reduced-activation ferritic-martensitic steels are promising candidates for applications in future fusion power plants. Samples of a reduced activation ferritic-martensitic 9 wt.%Cr-oxide dispersion strengthened Eurofer steel were cold rolled to 80% reduction in thickness and annealed in vacuum for 1 h from 200 to 1350 deg. C to evaluate its thermal stability. Vickers microhardness testing and electron backscatter diffraction (EBSD) were used to characterize the microstructure. The microstructural changes were also followed by magnetic measurements, in particular the corresponding variation of the coercive field (Hc), as a function of the annealing treatment. Results show that magnetic measurements were sensitive to detect the changes, in particular the martensitic transformation, in samples annealed above 850 deg. C (austenitic regime).