Application of the master curve methodology to fracture toughness characterization of ferritic-martensitic steel

Recent advances in fracture toughness have led to employment of the Weibull statistic to model scatter of fracture toughness in the transition region of low-alloyed ferritic steels. This methodology uses a concept of the universal temperature dependence of fracture toughness in the transition region, the so-called "master curve". The current physical background for this methodology suggests that it is applicable to a wide variety of ferritic bcc steels, including tempered ferritic-martensitic steels. Those steels are structural material candidates for fusion reactors. However, irradiation embrittlement (shift of the ductile-to-brittle transition region) of these steels is one of the main concerns for application purposes. Yet, the transition fracture toughness data for this class of steels are rather sparse. In this study, two types of fracture toughness specimens of a F82H steel were tested to verify the master curve concept. Specimens were tested at several temperatures in the transition region and at least four specimens were tested at each temperature allowing for application of the Weibull statistic/master curve analysis procedure. The largest specimens were 1T compact specimens. Broken halves of 1T specimens were later used to machine and test smaller, 0.4T, size specimens which could be more suitable for irradiation experiments. It was shown that scatter of fracture toughness of this material was rather high relative to scatter of low-alloyed steels but it was similar between larger and smaller specimens.