Small-angle neutron scattering applied to low-dose neutron-irradiated Fe–Cr alloys and ferritic martensitic steel Eurofer97

Abstract Experimental results reported before for neutron-irradiated binary Fe-Cr alloys and high-dose neutron-irradiated ferritic/martensitic (F/M) Cr steels do not unfold a complete understanding of the irradiation behaviour required for the application of F/M steels in nuclear components. Gaps are related to the effect of secondary alloying and impurity elements, such as Ni and Si, as well as the dose dependence at lower neutron doses, e.g. the range 0.1 – 1 displacements per atom (dpa). Such input is essential for both multiscale modelling of irradiation effects and the evaluation of nuclear fission or fusion components at the first stages of operation. Using magnetic small-angle neutron scattering, three pieces are added to the puzzle: (1) The effect of Cr undersaturation (5% Cr) and supersaturation (14% Cr) on the formation of irradiation-induced solute atom clusters/precipitates in the presence of intentionally added levels of Ni, Si, and P; (2) the effect of irradiation temperature, 290 °C versus 450 °C; and (3) a comparison of two heats of Eurofer 97, one of them neutron-irradiated to 0.06, 0.1 and 0.6 dpa. We have found that the irradiation-enhanced formation of Cr-rich α’-phase particles is the dominant effect for supersaturated Fe-14Cr-NiSiP. In contrast, α’ formation is impossible in Fe-5Cr-NiSiP, for which the pronounced irradiation effects observed at 0.1 dpa are mainly due to added Ni, Si and P. Finally, the 9Cr steel Eurofer 97 exhibits a much smaller irradiation effect than Fe-9Cr-NiSiP. The reasons of this exceptional irradiation resistance are discussed.