Abstract
This work investigates the effect of Al additions on the hydrogen embrittlement behavior of a generic Fe-0.4C steel. It is found that when 2wt.% Al is added to an Fe-0.4C steel, a very thin ferritic film is formed on the prior austenitic grain boundaries. This microfilm is formed since Al is a ferrite stabilizing element. Although both materials have a similar bulk hardness, the presence of the ferritic film causes a strong increase in ductility when tested in air. When hydrogen is added, the interface between the ferritic film and the martensitic matrix becomes the preferential fracture propagation path which results in an intergranular fracture surface. This can be linked to an interplay between the hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanism which causes a hydrogen induced decohesion of the ferrite/martensite interface. For the Al-free martensitic steel, without grain boundary ferrite, fracture in the presence of hydrogen occurs at lower extension values and causes a brittle cleavage type of fracture due to the embrittlement of the martensitic packets/blocks according to the HEDE mechanism. So, the addition of Al can increase the resistance to HE by redirecting the hydrogen induced crack propagation along the interface of the Al-induced ferritic microfilm.