Assessment of Mechanical Properties and Microstructure of EUROFER97 Steel after Thermo-Mechanical Treatments

EUROFER97 martensitic steel is recognized in EU as the reference material for the test blanket module in ITER reactor and for structural sections subject to high radiation doses in DEMO reactor. An extended experimental campaign has been carried out with the scope of improving strength without loss of ductility. The main idea behind the present study is to reach the goal through grain refinement achieved by cold rolling and heat treatments for inducing recrystallization of the work hardened structure. A combination of five cold rolling reduction ratios (CR) (20%, 40%, 50%, 60%, 80%) and eight heat treatments in the temperature range 400-750°C (steps of 50 °C) with soaking time of 1 hour has been examined to describe the evolution of microstructure and mechanical properties. The strength of deformed samples decreases as the heat treatment temperature increases and the change is more pronounced in the samples cold-rolled with higher CR ratios. The results showed that cold rolling with CR of 80% followed by a treatment at 650 °C produces a fully recrystallized structure with sub-micrometric grains which guarantees improved yield stress and hardness than standard EUROFER97 steel, with a comparable total elongation. In conclusion, this work demonstrated the feasibility to strengthen EUROFER97 without compromising its ductility.