Effects of specimen size on fracture toughness of phosphorous added F82H steels

Reduced-activation ferritic (RAF) steels are promising candidate structural materials for fusion reactor blanket components. However, a large amount of He on grain boundaries over 550–700 appm may cause non-hardening embrittlement (NHE) on the RAF materials. Therefore, understanding the fracture toughness on the RAF steels are critical in design and operation of the reactor. In the present study, constitutive data and widely obtained fracture toughness data sets at transition temperatures of F82H are investigated to establish the master curve method for RAF steels from viewpoints of fracture mechanics. For effective production of irradiation database, small specimen tests is applied to evaluate fracture toughness properties for F82H steels with different levels of phosphorous addition so that it can simulate the effect of fracture mode change from cleavage to intergranular fracture on the shift of transition curve. In this study, effects of specimen size and phosphorous on fracture toughness are also evaluated using the different size specimen (1 CT, 1/2 CT and 1/4 CT). As a result, phosphorous added steels show intergranular fracture in a brittle manner even in temperatures of transition region. The master curve approach is used here for evaluation of fracture toughness change by the degradation of grain boundary strength based on the ASTM E1921.