R omain Chochoy

Abstract

The design of a liquid hydrogen tank requires a good comprehension of the influence’s factors of crack initiation and propagation under hydrogen at cryogenic temperatures. Indeed, the hydrogen embrittlement (HE) is the main damage mechanism observed. Therefore, it is necessary to improve the understanding of the main parameters governing the HE in fatigue at cryogenic temperatures. In this context, the work conducted in this study focuses on the interaction between hydrogen and crack initiation at different loads and the determination of the fatigue life associated.

During their life, the components endure a high temperature range (between -253°C and 25°C) which induce properties variations. Indeed, one of the parameters contributing to these phenomena is the martensite transformation (MT), when the temperature is decreasing, the transformation is facilitated. At -120°C, for two different steel grades (304L and 316L Stainless steel), the MT become spontaneous, it means that only de temperature is governing the phase transformation between austenite and martensite, this temperature is called M_s. In hydrogen environment, the maximum hydrogen embrittlement is observed at -120°C. It seems that below this temperature, HE is controlled by the MT and above HE is controlled by the hydrogen diffusivity. It is necessary to conduct test at M_s  temperature and above in different environments (air, hydrogen, nitrogen) to evaluate the embrittlement only induced by MT and not by the environment. The first stage of this work focused on the fatigue behaviour at room temperature in air, self-heating and ratcheting were studied.

Session