Microstructural and Mechanical Characterization of the Radiation Effects in Model Reactor Pressure Vessel Steels

This paper presents results of radiation-induced nanoscal microstructural changes measured by Small-Angle Neutron Scattering (SANS) on ASTM-type reactor pressure vessel (RPV) steels. Five different base metals and one weld metal were investigated. The irradiation was performed in a VVER-type power reactor on 3 different dose levels, maximally 0.14 dpa, at an irradiation temperature of 255 °C. The volume content of the micostructural features measured is correlated with the irradiation hardening and embrittlement.
In every case clear radiation-related hardening, embrittlement and microstrucural effects are proven. Radiation produces nanoscaled scattering defects of a radius between 0 < R < 3 nm with the maximum near R = 1 nm. Fluence and chemical composition do not or hardly change the shape of the size distribution but strongly the volume content. The radiation sensitivity is mainly controlled by the copper content. Copper also increases the A-ratio. There are good correlations between volume content of the nanoscaled radiation defects and the radiation hardening or embrittlement, respectively.
Annealing at 475 °C produces almost full recovery of the mechanical properties. However, the original microstructure of the unirradiated state is not completely reproduced.