Fatigue Behaviour of a 9Cr1MoNbV Martensitic Steel in a Liquid Metal*

Abstract The low cycle fatigue behaviour of the T91 martensitic steel is studied in the range Δε t from 0.4% to 2.4%, at 300°C, in air and in liquid Lead Bismuth Eutectic (LBE). It is shown that the cyclic stress response consists of a cyclic softening that is not modified by the environment. However, the fatigue life is reduced after fatigue in LBE as compared to air and the effect is especially marked at high strain range. Metallographic analysis of the external surfaces and of transverse cross sections of specimen show that the short crack density is very low in the specimen failed in liquid metal while it is high for tests in air. Fracture surface observations show that multiple crack initiations occurred in air. In liquid metal, the fracture surfaces were flat and contained widely spaced fatigue striations. Strain localization promoted by the liquid metal is responsible for the decrease in fatigue resistance.