Corrosion resistant steel sheet with a chemically modified zinc coating

摘要

A new processed steel sheet comprises a steel base coated with a Zn or its alloy plating layer and a converted layer, which contains both of at least an insoluble or scarcely-soluble metal compound and at least a soluble metal compound. The insoluble or scarcely-soluble compound may be one ore more of valve metal oxides or hydroxides, and the soluble compound may be one or more of valve metal fluorides. The converted layer may be also composed of one ore more of complex compounds of Mn and Ti. The insoluble or scarcely-soluble compound acts as a barrier for insulation of a steel base from an atmosphere, while the soluble compound exhibits a self-repairing faculty to repair defective parts of the converted layer. Due to the converted layer, the processed steel sheet is remarkably improved in corrosion resistance, without presence of chromium compounds which would put harmful influences on the environment.