Abstract
17-4 PH grade is a precipitation-hardened martensitic stainless steel characterized by high ultimate tensile strength coupled with good corrosion resistance in aqueous media. Nevertheless, it is known to be extremely susceptible to hydrogen which limits its potential use for hydrogen-based mobility applications. Therefore, 17-4 PH alloy was studied in order to investigate interactions between hydrogen and microstructural elements which can lead, in certain circumstances, to the material failure. The experimental approach combined physicochemical characterizations (optical microscopy, X-Ray Diffraction, Transmission Electron Microscopy coupled with ASTAR) and electrochemical permeation measurements conducted on different heat treated samples (solution annealed, low temperature aged, high temperature aged, double aged). Depending on the microstructure, the apparent hydrogen diffusivity (~ 10-13 m2.s-1 at 23 °C) was significantly modified. More specifically, copper precipitates appeared to be effective trapping sites for low temperature ageing condition while austenite contributed to slow down hydrogen diffusion for double ageing condition.