A microstructural based understanding of hydrogen-enhanced fatigue of stainless steels

The microstructure immediately beneath the fracture surface produced during fully-reversed fatigue loading of uncharged and hydrogen-charged 304 and 316 stainless steels has been investigated by using focused ion beam machining in conjunction with transmission electron microscopy. The microstructure beneath striations on the fracture surface is dependent on the presence/absence of hydrogen and varies as a function of distance from the surface. The underlying microstructure also is dependent on the morphology of the fracture surface and is distinctly different beneath striations and flat regions. The differences in evolved microstructure are considered in terms of mechanisms by which hydrogen modifies deformation processes.