Origin of hydrogen embrittlement in ferrite-martensite dual-phase steel

Different ferrite-martensite dual-phase (DP) steel microstructures were subjected to controlled electrochemical hydrogen charging followed by tensile deformation. An increase in hydrogen content enhanced strengthening and dynamic recovery, but lowered non-uniform elongation. Hydrogen embrittlement originated from the severity of microscopic post-necking strain localizations in the ferrite phase, and preferential/accelerated damage initiation at the ferrite-martensite boundaries. Atomistic diffusion-based hydrogen concentrations, at different microstructural features, were captured by multi-scale molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. The hydrogen content, in particular, reduced with an increase in martensite tetragonality. This, in turn, enhanced the phase boundary hydrogen concentrations leading to interface decohesion.