Correlation between irradiation-induced changes of microstructural parameters and mechanical properties for RPV steels

Radiation hardening, displayed by the yield stress increase, and radiation embrittlement, described by the Charpy transition temperature shift, were experimentally determined for a broad variety of irradiation probes machined from different reactor pressure vessel base and weld materials and irradiated in several VVER-type reactors. Additionally, the same probes were investigated by small angle neutron scattering. The analysis of the neutron scattering data suggests the presence of nanoscaled radiation defects. The volume fraction of these defects depends from the neutron fluence and the material. Both radiation hardening and radiation embrittlement correlate with the square root of the defect volume fraction linearly. However, a generally valid proportionality is only a rough approximation; in detail chemical composition and technological pretreatment clearly affect the correlation.