Low-pressure diffusion chromising of thin low-carbon steel sheet for improved surface and bulk properties

Multi-component alloying of thin metal sheets offers the particular possibility to produce novel materials with adjusted bulk and surface performance characteristics. Its application is of great interest for the development of advanced materials with tailored properties such as steel based materials for the use as bipolar plates for proton exchange membrane fuel cells. Within this work 0.13-mm thick cold-rolled sheets of low-carbon steel EN 1.0338 were double-sided chromised by means of low-pressure diffusion metallization method. Samples with chromium diffusion coatings as well as bulk-chromised samples, i.e., samples fully chromised over the whole strip thickness, were prepared. For the diffusion coefficient of chromium in γ-iron phase at 1423 K a value of 1.80·10−14 m2 s−1 was determined. As long as the samples did not reach the bulk-chromised state, the chromium concentration remained less than 12.5 wt%. The bulk-chromised sheets with surface chromium concentration of approximately 22 wt% showed the best corrosion resistance in 0.5% sodium chloride and 0.05 M sulphuric acid solutions electrochemical tests. Moreover, they exhibited the smallest interfacial contact resistance of approx. 31 mΩ cm2 at a contact pressure of 140 N cm−2.