Reflection of the changes in properties of pressure vessel metal due to irradiation, recovery annealing and re-irradiation in the character of fractures obtained in Charpy impact testing

Pressure vessel steels of Russian and American origin were investigated by raster electron microscopy (fractography), optical microscopy (metallography) and transmission electron microscopy (TEM). The influence of Russian weld macrostructure parameters on the data obtained by Charpy test was revealed. Possible appearance of brittle intergranular components in fracture surfaces of sub-size Charpy specimen made of Russian weld metal with phosphorus content greater than 0.04% was shown when tested at temperatures close to the upper shelf level. Recovery annealing at 475 deg.C, for 15 hours did not induce reduction of the brittle intergranular component while recovery of DBTT was observed. This confirmed that the contribution of radiation induced intergranular phosphorus segregation to embrittlement of pressure vessel steels is not significant. The presence of ductile intergranular component in fractures of specimens made of Russian and American steels confirmed the possibility of radiation induced intragranular phosphorus segregation to precipitate/matrix interfaces. In accordance with the properties recovery due to annealing, the successive reduction of ductile intergranular component fraction in fracture surfaces indicates that the contribution of radiation induced ill-treating phosphorus segregation to radiation embrittlement of pressure vessel steels is valuable