Microstructural evolution of ferritic-martensitic steels irradiated in the fast breeder reactor Phénix

Abstract This paper deals with the microstructural evolution of a 17Cr ferritic steel (F17) and five stabilized (EM12, FV448, HT9 and 1.4914) or unstabilized (EM10) 9–12Cr ferritic-martensitic steels irradiated in Phenix. The TEM examinations performed on these steels show that their microstructures are only modified by irradiation at low temperature ( T C ). Few voids are generally observed, leading to swelling values close to zero, except in duplex EM12 and ferritic F17 steels. On the other hand, fine and uniform precipitation of α', M 6 C and χ-phases is induced by irradiation in alloys that contain either more than 13% Cr (α'), or more than 0.3% Ni (M 6 C) or 2% Mo (χ). This precipitation coupled with the radiation-induced dislocation microstructure, is responsible for radiation-induced embrittlement which depends both on number density and nature of particles, α' being more detrimental than M 6 C or χ.