REDUCTION OF DISCOLORATION OF ELECTROCHEMICALLY TREATED CHROMIUM ELECTROPLATED FERROUS METAL STRIP

摘要

Discoloration of ferrous metal strip electroplated with metallic chromium in a continuous electroplating line at high line speeds and then electrochemically treated to deposit a nonmetallic chromium containing film thereover is reduced by intimately contacting the metallic chromium plated strip with an aqueous solution of a water soluble hexavalent chromium compound prior to the electrochemical treatment. The aqueous solution preferably has a composition which is substantially the same as the chromium electroplating electrolyte. The invention is especially useful in producing tin free ferrous metal container stock having a composite protective coating including an undercoating of 0.1-0.5 microinch of metallic chromium and an overcoating containing chromium oxide.