Fracture properties of notched and pre-cracked specimens of a tempered martensitic steel at low temperature

The fracture properties of the 9CrWVTa reduced-activation tempered martensitic steel Eurofer97 were studied in the lower ductile to brittle transition. Sub-sized pre-cracked compact tension and notched tensile specimens were tested. Finite element simulations were undertaken to supplement the mechanical tests and to calculate the local stress/strain fields around the stress concentrators. Based upon a local approach of quasi-cleavage, a critical stress state was calibrated on the fracture toughness data measured with the compact tension specimens. This critical stress state was shown to predict the evolution with temperature of the lower bound curve of fracture toughness data. It was also found to predict very well the failure load and failure displacement of the notched specimens.