In this study, the effect of a high temperature nitriding treatment on the characteristics of the Ni-free stainless steel (SUS445) used as the metallic bipolar plate of a polymer electrolyte fuel cell (PEFC) was investigated. The phase structure, composition, electrical conductivity and electrochemical corrosion resistance of the stainless steel after the nitriding treatment (SUS445-N) were analyzed. The supersaturated nitrogen phase gamma(N), nitrides CrN and Cr2N in the nitride layer with a good electrical conductivity were observed and confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the nitrided SUS445-N stainless steel was significantly improved due to the formation of the chromium-containing nitrides. The conducted fuel cell durability test revealed that when using the nitrided SUS445-N stainless steel as the bipolar plate, the fuel cell voltage performance was almost the same as that using the graphite carbon as the bipolar plate for 2500 h. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.