Ductile-to-brittle transition of low activation ferritic–martensitic steels with respect to critical cracks promoting final brittle fracture

9–11 wt.%Cr ferritic–martensitic steels with fine carbide structures are considered as potential candidates for the blanket and first wall structures of fusion reactors. Charpy impact tests have been performed in the ductile-to-brittle transition temperature range of these steels in such a way that a dynamic quasi-equilibrium has been achieved in the process zones of the investigated specimens prior to brittle failure. This type of testing enables the evaluation of dynamic Weibull moduli and, consequently, dynamic Weibull master curves,which provide the failure probability densities of the investigated steels as functions of the scaled, critical crack-sizes.