The effect of hydrogen on the deformation of pearlite in steels

Hydrogen embrittlement in steel gas infrastructure is a serious challenge for the use of hydrogen energy for global decarbonization. Steel gas pipelines contain a significant fraction of pearlite, which consists of lamellar cementite in ferrite. How exactly hydrogen affects deformation and failure in this structure, and hence the role that pearlite plays in embrittlement, is not well understood. Here we have studied the behavior of hydrogen around the cementite–ferrite interface, the defining microstructural feature in pearlite. Our micromechanical testing results show softening in the ferrite adjacent to the interface, consistent with hydrogen-enhanced local plasticity, rather than interfacial weakening. Atom probe tomography (APT) observations of hydrogen at the interface show no evidence of trapping at the cementite–ferrite interface, instead hydrogen trapping in pearlite occurs in the cementite bulk. Density functional theory calculations, accounting for the configuration of the lattice defects and local interfacial misfits, are consistent with the experimental observations. These findings explain how hydrogen leads to degradation in pearlite. This information is critical for the development of next-generation pipeline materials that can better withstand hydrogen embrittlement.