Plasma nitrided austenitic stainless steels for automotive hydrogen applications

This work is focused on the development of plasma diffusion treatments for stainless steels to obtain a higher conductivity of bipolar plates in fuel cells and secondly, to avoid hydrogen embrittlement of stainless steels in case of high pressure hydrogen storage systems by the formation of a single γ C layer. Electrical conductivity and corrosion resistance were enhanced by plasma nitriding. Tests with single cells have shown a 15% higher voltage compared to graphite plates at low temperatures and reduced treatment durations. The substitution of high alloyed stable stainless steel grades by cheaper metastable stainless grades depends on a successful suppression of hydrogen environmental embrittlement. A promising way could be a surface treatment resulting in the formation of a γ C layer on top of the surface. Plasma nitrocarburizing can form such γ C layer, but a variation of treatment temperature and CH 4 content was not successful in suppressing the undesired S-phase as a top layer.