High temperature microstructural evolution and mechanical behaviour of the 16MND5 pressure vessel steel during a severe nuclear reactor accident

This study deals with the steel 16MND5 used for the vessels of the PWR type reactors. During accidents this low carbon steel microstructure changes. The thesis deals with the austenitic phase and with the aging of the initial microstructure. The austenite grain size evolution has been described and a model is proposed to simulate the growth kinetic. The austenitic phase behaviour at high temperature creep is observed. The model proposed by Lasalmonie and Strudel agrees the experimental results. This model is based on the dislocations increase in the context sliding at the grain boundaries and allows to take into account the grain size influence. During the aging of the 16MND5 at 700 C, a microstructural hardening is observed. This hardening is bound to long white phases formation and growth. (A.L.B.)