Critical hydrogen concentration for crack propagation in a CrMo steel: Targeted experiments for accurate numerical modelling

This study focuses on CrMo steel experiencing decohesion mechanism in presence of hydrogen. A tailored experimental characterization is performed with tensile, permeation and toughness experimental tests to obtain all the inputs for the numerical simulations of a propagating crack in a C(T) specimen. The used finite element framework is based on the cohesive zone modelling. The aim of the numerical model and of the work is the identification of a critical hydrogen concen-tration inducing crack tip propagation. Given the tailored inputs, these models accurately esti -mate the hydrogen concentrations in the lattice and the reversible traps, and follow their redistribution along the ligament during the time. From the obtained results, we could quantify that a decrease of two orders of magnitude in the test speed reduces the critical hydrogen con-centration at the crack tip, necessary to activate the failure of the first cohesive element and therefore the propagation, from 0.994 to 0.784 wppm, that is-21%.