The microstructure associated with the hydrogen-induced features flat and quasi-cleavage on the fracture surface of a lath martensitic steel has been visualized in a transmission electron microscope by using focused-ion beam machining to extract samples perpendicular to the fracture surface. Beneath both hydrogen-induced fracture surfaces there is direct evidence, in the form of intense slip bands and destruction of lath boundaries, for significant plasticity. These observations are considered in terms of the fundamental hydrogen embrittlement mechanisms, and the conclusion is reached that the failure is driven by a hydrogen-enhanced and plasticity-mediated decohesion mechanism.
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