On the transition toughness of two RA martensitic steels in the irradiation hardening regime: a mechanism-based evaluation

An analysis of the transition fracture toughness and constitutive behavior of F82H and Eurofer97 reduced activation martensitic steels are presented in both unirradiated and irradiated conditions. The unirradiated toughness data for F82H show very steep temperature dependence and the Eurofer97 toughness data measured with 5 mm versus 10 mm thick specimens are systematically higher. Both of these observations indicate a loss of constraint. Constraint loss adjustments are applied using a three-dimensional finite element analysis based toughness scaling model. The adjusted F82H results can be represented by a master curve (MC) and the corresponding 5 and 10 mm adjusted data fall in the same scatter band. The 10 mm irradiated specimens, with generally lower toughness levels, suffer minimal constraint loss. The irradiation induced MC T0 shifts (ΔT0) are analyzed in terms of changes in constitutive properties. The ΔT0 are generally consistent with the observed irradiation hardening. However, the effects of irradiation on post-yield strain hardening behavior must be considered to obtain self-consistent hardening-shift relations.