Study of the influence of current density and displacement rate on hydrogen embrittlement using small punch tests

Susceptibility to hydrogen embrittlement was studied on quenched and tempered 42CrMo steel with Small Punch Tests (SPT) using different punch displacement rates. Hydrogen was cathodically charged using an electrolyte composed of 1 M H2SO4 with 0.25 g/l As2O3, and two different cathodic current densities (0.50 and 1.00 mA/ cm2). The results were analysed using different embrittlement indices: related to the energy consumed at maximum load, to the equivalent biaxial deformation at failure location and to the failed diameter. Failure location is directly related to punch displacement and, consequently, to embrittlement. All embrittlement indices increase as the punch displacement rate decreases (longer time for hydrogen diffusion) and as the cathodic current density increases (higher hydrogen concentration in equilibrium with the hydrogenated medium). On the other hand, the use of a pre-charging time before the start of the in-situ hydrogen charged test produces no change in the results, as most hydrogen enters the sample due to the high plastic deformation induced on its surface in the course of the mechanical test.