Integrated experimental and multi-trapping finite element approach to estimate critical hydrogen concentrations and embrittlement in CrMo steel

The paper presents a numerical study on a CrMo martensitic steel experiencing hydrogen embrittlement with enhanced localized plasticity mediated by decohesive mechanisms. Experimental inputs, including stress-strain curves, trap energies and densities, initial hydrogen concentration CL0 and diffusion coefficient, were inputted into a cohesive zone model. The model suggests quantifying embrittlement with three parameters: the critical concentration at the tip, the concentration peak ahead of the tip and the distance of the peak from the tip. The simulations at the two test speeds of 1 and 0.01 mm/min revealed that dislocation traps dominate at the crack initiation, with a critical hydrogen concentration at the tip of 2.5 CL0, independent of the test speed. As propagation advances, the critical hydrogen concentration decreases to the asymptotic value of 1.5 CL0. This trend changes as a function of the test speed: the lower the speed, the higher the time hydrogen has to move to the tip, t...