Characterization of Ion Irradiation Effects on the Microstructure of 316 Austenitic Stainless Steel

Internal structures of Pressure Water Reactors (PWR) are maintained by bolts made of 316 austenitic stainless steel (SS). They are subjected to neutron irradiation, which can lead to the cracking of bolts by the complex phenomenon of Irradiation Assisted Stress Corrosion Cracking (IASCC). One of the origins of IASCC is the evolution of the steel microstructure during irradiation.In order to get a better understanding of irradiation effects on the microstructure of austenitic SS, model alloys (FeCrNi, FeCrNiSi) and 316 austenitic SS were ion irradiated at 200 degree C and 450 degree C, up to 5 displacements per atom (dpa). Complementary techniques were used to characterize the steel: Atom Probe Tomography to quantify local chemical changes, Transmission Electron Microscopy to get information about defects clusters (loops and cavities) and Positron Annihilation Spectroscopy to characterize vacancy type defects.The experimental results, obtained in the PERFORM60 European project, will be detailed and discussed in this talk.