Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Reactor pressure vessel (RPV) steels in nuclear reactors face embrittlement due to neutron irradiation. The embrittlement is associated with an increase in the reference temperature obtained via fracture toughness testing using the Master Curve concept. However, the fracture surfaces of some highly embrittled RPV steels exhibit ductile dimples. Through this work, we show that material properties, such as yield strength as a function of temperature, play an important role in determining the net hardening of a material. Additionally, we recorded the location of fracture initiators, using scanning electron microscopy (SEM) on the fracture surfaces of tested mini-C(T) specimens from four different RPV steels, to check whether it was affected by neutron irradiation and side grooving. We detected fracture initiators associated with high fracture toughness at greater distances to the crack tip. The locations of the fracture initiators changed significantly for samples with and without side-grooves and did not change significantly with respect to the irradiation state. We found the primary causes for increased ductility of embrittled RPV steels to be lower irradiation induced hardening and a higher loss in yield strength with increasing temperatures. Caution must therefore be exercised while interpreting the embrittlement of a material using ductile fracture surfaces alone.