Volume 2, Issue 10 (November 2005)
Microstructural and Mechanical Characterization of Radiation Effects in Model Reactor Pressure Vessel Steels
This paper presents results of radiation-induced nanoscale 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 to three 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 nanoscale 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 influence the volume fraction. The radiation sensitivity is mainly influenced by the copper content. Copper also increases the A-ratio. There are good correlations between volume fraction of the nanoscale radiation defects and the radiation hardening or embrittlement.
Annealing at 475°C produces almost full recovery of the mechanical properties. However, the original microstructure of the unirradiated state is not completely reproduced.