Hydrogen Embrittlement in Super Duplex Stainless Steels

The ductility of materials can be reduced by hydrogen. Such reduction can result in a form of premature failure often termed as hydrogen embrittlement. In super duplex stainless steels, although both austenite and ferrite are susceptible to hydrogen embrittlement, there is a lack of understanding into the hydrogen embrittlement contribution of each phase. In this study, in situ neutron diffraction tests were applied on H-charged samples to investigate the hydrogen embrittlement behaviour in super duplex stainless steels. The result reveals that austenite maintains good plasticity during tensile testing, whilst a loss of it is realised in ferrite. Fractography analysis reveals that there is a brittle-to-ductile transition from the sample surface towards the centre; hydrogen embrittlement vanishes as the specimen's centre is approached, while it is demonstrated to disappear first in austenite but not in ferrite. This transition can be predicted by applying a physics-based hydrogen embrittlement model which incorporates the effects of hydrogen concentration, hydrogen diffusivity, residual stress, loading state and temperature. The present work demonstrates the dissimilar susceptibility of austenite and ferrite to hydrogen embrittlement, providing a tool to describe it.