This study focuses on the production of high-nitrogen stainless steel by solution nitriding as a low-cost and mass-production of bipolar plates for PEFCs. We investigate the effect of nitrogen pressure during heating on the corrosion resistance and contact resistance of high-nitrogen stainless steels. In the solution nitriding of 22Cr ferritic stainless steel, higher nitrogen pressure promoted austenitization of the matrix phase and improved corrosion resistance. However, much higher nitrogen pressure promoted the coarsening of nitrides on the surface and reduced corrosion resistance.

Rust structure on carbon steel coated with cellulose nanofiber dispersion resin containing nickel sulfate was investigated after corrosion under repeated dry and wet conditions. X-ray diffraction and electrochemical measurements were performed to evaluate the rust composition and anticorrosion properties of the rust layer. It was found that the proportion of stable α-FeOOH increased, especially with the addition of nickel sulfate. The decrease in corrosion rate might be due to the increase in mass fraction of α-FeOOH.

Slow strain rate test （SSRT） was performed for a rolled carbon steel in NaHCO₃ aqueous solutions at various temperatures in the range of 303-393 K. Selected concentrations of NaHCO₃ between 0.1 and 0.5 mol･dm^－3 are assumed to be the upper limit of carbonate concentration in groundwater in a geological disposal environment. As the results, no obvious influence of temperature on mechanical properties such as fracture strain ratio were observed, but SCC susceptibility based on ratio of SCC fracture area increased at relatively low temperatures of 303 K and 323 K. It was suggested that the reason for the higher SCC sensitivity of the steel at lower temperatures was due to slower repassivation at lower temperatures. Regarding the type of SCC, intergranular SCC was dominant at low temperatures and tended to transition to transgranular SCC at higher temperatures.