Effect of the composition on the behavior of Fe-9Cr steels after n-irradiation

High Chromium ferritic/martensitic (F/M) steels are considered as the most promising structural materials for future nuclear power plant systems such as Accelerator Driven Systems (ADS), fusion, and GENIV. The selection of these materials is based on the studies performed on commercial Cr-Mo steels considered for fast breeder reactors in the early 70s. Within the fusion community, a substantial effort has been made to modify the basic composition not only to lessen the environmental impact of the irradiated steels but also to improve their properties. Thus, one of the major drawbacks of this selection is the significant hardening and embrittelment of these materials, caused by neutron irradiation at low temperatures. To mitigate this phenomenon or at least to predict its occurrence, it is highly recommended to study the fundamental issues related to radiation damage both experimentally and theoretically. This paper reports on the performance of the newly developed steel at Europe namely Eurofer 97, which was irradiated, characterized and tested under the same conditions as its 'grand-father' T91 and a binary alloy containing similar concentration of the main alloying element Cr. The irradiation has been performed at the Belgian reactor BR2, at 300 degree C for doses ranging from 0.06 dpa up to 1.5 dpa. The results demonstrate the effects of the chemical composition on the morphology, size and density of the defects created. Further, the hardening of the materials appears to be strongly dependent on dose and on chemistry. It will be shown that the defect loops observed by Transmission Electron Microscopy (TEM), cannot explain alone the hardening observed but the local short range ordering should play a substantial role. (authors)