Investigation of the Microstructure Factors Affecting the Brittle Fracture Initiation of Pre-Cracked Charpy-Type Samples of VVER-1000 RPV Steel

The correlation between fracture toughness parameter KJc and cleavage initiation distance (CID) for the three point bending (3PB) pre-crecked Charpy type specimens of VVER-1000 reactor pressure vessel base and weld metals was observed. Two types of brittle fracture origin sites were found: nonmetallic inclusions and grain or subgrain boundaries. It was shown that KJc values are shifted to the higher temperature area for weld metal with respect to base metal data. In case when the initiation origin is grain or subgrain boundary, the KJc values are higher for base metal at the same CID values. This indicates the higher crack resistance of base metal.