3. Mechanical behavior of metal alloys under H2 pressure

Hydrogen embrittlement is characterized by a drop in ductility, toughness and an acceleration in the rate of fatigue crack propagation, resulting in a shorter component life under cyclic loading. The sensitivity of a material will depend on its microstructure (chemical composition, phases, defects...), gaseous environment (partial pressure of H ₂ , impurities), mechanical stress (stress rate, monotonic or cyclic loading...) and the presence of stress concentration zones (notch or crack). The remainder of this chapter presents the main characteristics of the mechanical behavior of different classes of metal alloys in the presence of hydrogen. As it cannot be exhaustive, the aim is to highlight the main trends observed, so as to provide the right approach for taking this particular environment into account when dimensioning a component.