Method for treating steel plate and its manufacture

摘要

This invention relates to the surface treatment of steel plates or sheets and discloses a novel steel sheet structure, wherein the steel sheet is first electrolytically surface coated with a metallic chromium layer of a thickness not exceeding about 0.1 micron and is then electrolytically plated with a chromate film of a thickness not exceeding 0.1 mg/dm2. The chromium layer thickness should preferably not be less than 0.0016 micron. The inventive steel sheet constitutes a superior can stock and may be provided with a top coat of organic composition. The invention also discloses a two-step process for producing the sheet. Pursuant to this process the metallic chromium layer is first electrolytically deposited on the steel sheet surface, whereupon the chromate film is electrolytically deposited on the metallic chromium layer. An important feature of the invention is that the chromate treatment is carried out in a solution which is devoid of a sulphuric acid radical having a tendency to deposit metallic chromium. Particular process conditions in respect to bath composition, current density and treatment time are disclosed.