The present invention provides a coating composition for forming a titanium oxide film, comprising (A) a specific titanium-containing aqueous liquid and (B) at least one compound selected from the group consisting of organic acids and their salts. The present invention also provides a process for forming a titanium oxide film using the coating composition, and a metal substrate coated therewith.
A surface-treated steel sheet is disclosed, including a zinc based plated steel sheet having thereon a surface-treated film containing titanium, nickel, aluminum and fluorine and having a film thickness of from 0.05 to 1.0 .mu.m, the surface-treated film having a titanium deposition amount of from 0.01 to 0.5 g/m.sup.2 and containing from 0.01 to 5 parts by mass of nickel, from 0.1 to 25 parts by mass of aluminum and from 1 to 500 parts by mass of fluorine relative to 100 parts by mass of titanium. This surface-treated steel sheet does not contain hexavalent chromium in the film thereof at all and has excellent heat discoloration resistance, corrosion resistance and resistance to blackening.
