MICROSTRUCTURAL EVOLUTION OF FERRITIC-MARTENSITIC STEELS IRRADIATED IN THE FAST BREEDER REACTOR PHENIX

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 < 500-degrees-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 alpha', M6C and chi-phases is induced by irradiation in alloys that contain either more than 13% Cr (alpha'), or more than 0.3% Ni (M6C) or 2% Mo (chi). 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, alpha' being more detrimental than M6C or chi.