Improvement in Atmospheric Corrosion Resistance of SUS 430 Stainless Steel by Plating

The atmospheric corrosion resistance of stainless steel is not so enough satisfactory that even SUS 304 rusts considerably in seaside district. Although Ni, Cr or Ni·Cr plating is expected to extremely improve this resistance, if the electrodeposited layer is broken down by various processing and so on, there is a danger that corrosion reaction proceedes more rapidly by galvanic corrosion. In this work, the investigation was done about this danger by estimating the degree of atmospheric corrosion resistance of SUS 430 which was electroplated with Ni, Cr or Ni·Cr, and extended to 10%, and then rusted by atmospheric corrosion test for 15 days, accelerating the corrosion reaction by spraying the artificial sea water provided by ASTM D-1141-52. Ni- plated SUS 430 corroded violently in particular when extended to 10% and Cr-plated SUS 430 rarely rusted. From the measurements of corrosion potential and galvanic current of specimen in the artificial sea water whose pH was exchanged from 8.2 to 1.0 by HCl, it was considered that the anodic reaction proceeded at the space under the dust or at the bottom of crack in which pH dropped under 2, and the cathodic reaction on Ni proceeded rapidly due to the absence of passive film, but this reaction on Cr hardly proceeded due to the existence of passive film.