Overview of gaseous hydrogen-assisted fatigue crack growth in ferritic iron and steels: Bridging micro and macro

Acceleration of fatigue crack growth in steels under hydrogenating environments (hydrogen-assisted fatigue crack growth, HA-FCG) is of critical concern for the defect-tolerant engineering design of pressure vessels and pipelines for the storage and transportation of gaseous hydrogen. This overview provides a state-of-the-art understanding of the HA-FCG in ferrite-based materials with a primary basis on the authors’ recent works. The influences of gas pressure, temperature, stress intensity, and loading frequency are summarized, focusing on two representative failure modes: intergranular (IG); and cleavage-involving transgranular (CIT). The latter one has conventionally been termed quasi-cleavage (QC). Crack path crystallography and deformation microstructures beneath these IG and CIT are provided as supplemental information to figure out the underlying fracture mechanisms. Comprehensive models accounting for the HA-FCG in ferrite are finally established. Our models construct new bridges between microscale fracture behaviors and macroscale dependencies of the FCG acceleration on environmental and mechanistic variables.