Origins of Brittle Microcracks in Crack Resistance Tests of Steels of VVER-1000 Vessel in Various States

摘要

In fractographic study of steels of nuclear reactor vessels after tests for crack resistance, two major sources of brittle destruction are detected: nonmetallic impurities and intergranular or subgranular boundaries. X-ray spectral microanalysis reveals that these are manganese sulfides and silicon oxides. The probable size of nonmetallic impurities (～1 μm) which can initiate brittle destruction is detected. The interrelation between critical stress intensity coefficient K_(Jc) and distance from "leader" to fatigue crack point CID (cleavage initiation distance) is considered. The influence of irradiation conditions on crack resistance of steels is demonstrated.