Precipitation Behavior of Irradiated Reduced-Activation Ferritic Steels.

Abstract

In order to study the effects of small additional elements on precipitation behavior in reduced-activation ferritic steels under neutron irradiation, analytical transmission electron microscopy was used to examine the microstructure and the precipitation of the extraction replica of several reduced activation ferritic/martensitic steels which have different contents of small additional elements after 60 displacements per atom (dpa) irradiation at 693, 698 and 733K in the Fast Flux Test Facility (FFTF)/Materials Open Test Assembly (MOTA). All of reduced-activation ferritic/martensitic steels were found to have a good phase stability after irradiation. Micro-voids were observed in both materials of Fe-9Cr-2W with or without boron, the density of micro-voids in the steel with boron is larger than that without boron, and the mean size of micro-voids is smaller than that without boron. However void swelling was less than 1%. Most of the precipitates in the irradiated specimens were found to be M23C6 which consists of mainly Cr. The remainder of the precipitates were found to be Ta-rich M6C. Laves phase was observed only at 733K. Several precipitates which were Ti-rich including Si and W were also observed at grain boundary in Ti addition steels at 733K irradiation. Several Y2O3 particles were observed in an yttrium containing alloy. No precipitation including Al was observed in an Al containing alloy. Ti addition decreased precipitation of Ta-rich M6C in 9Cr and 12Cr steels in this irradiation condition.