May L. Martin, Matthew J. Connolly, Frank W. DelRio, Andrew J. Slifka
The deleterious effects of hydrogen on the physical properties of metals have been known for over a century. Despite extensive work over that time period, there are still significant questions related to the hydrogen embrittlement of ferritic steels due to specific challenges associated with these steels coupled with the global difficulties with gauging hydrogen content in all materials. However, recent advancements in experimental tools and multi-scale modelling are starting to provide direct insight into the embrittlement process. This review focuses on a subset of the recent developments, with an emphasis on how new methods have improved our understanding of the structure-property-performance relations of ferritic steels subjected to mechanical loading in a hydrogen environment. The structure of ferritic steels in the presence of hydrogen is described in terms of the sorption and dissociation processes, the diffusion through the lattice and grain boundaries, and the hydrogen-steel interactions. The properties of ferritic steels subjected to mechanical loading in hydrogen are also investigated; the effects of test conditions and hydrogen pressure on the tensile, fracture, and fatigue properties of base metal and welds are highlighted. The performance of steels in hydrogen is then explored via a comprehensive analysis of the various embrittlement mechanisms. Finally, recent insights from in situ and high-resolution experimentation are presented and suggestions for future studies to address specific challenges related to embrittlement in ferritic steels are proposed.