Master Curve testing on WWER-440 reactor pressure vessel steels

The Master Curve (MC) approach used to measure the transition temperature, T0, was standardized first-time in the ASTM Standard Test Method E1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred cubic (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
Charpy size SE(B) specimens of base and weld metal from the WWER-440 Greifswald Unit 8 RPV were tested according to the ASTM test standard E1921-05. The measured fracture toughness values at brittle failure (KJc) of the specimen show a large scatter. In general the KJc values of the RPV weld and base metal follow the trend of the MC. For two base metals more than 5% of the KJc values lie below the 5% fracture probability line. It is therefore suspected that the investigated WWER-440 RPV base material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data and the nature of inhomogeneity was investigated.