Work-hardening behavior of cold rolled EUROFER97 steel for nuclear fusion applications

The reduced activation martensitic steel EUROFER97 is recognized in Europe as the reference steel for structural applications in future nuclear fusion reactors.

Usually, EUROFER97 steel plates are manufactured by hot rolling and successive heat treatments: (1) austenitization at 980°C for 30 minutes, (2) air cooling and (3) tempering at 760°C for 90 minutes. Recently, thermo-mechanical treatments have been investigated by us with the scope to improve the mechanical properties, namely to strengthen the steel without reducing its ductility. The experiments involve cold rolling with three reduction rates (30%, 40%, 50%) and, for each of them, heat treatments at different temperatures in the range from 550 °C to 750 °C. The mechanical and microstructural characterization of the samples after successive stages of the process is now underway and present work reports some preliminary results.

The characteristics of the samples after cold rolling have been examined by means of hardness tests, metallography and X-ray diffraction measurements and work-hardening is discussed in terms of grain refinement and dislocation density.