Chromate-treated zinc-plated steel strip and method for making
AssigneeKawasaki Steel Corporation
InventorsYuko Takeuchi, Yuki Nakahara, Hajime Kimura, Shinobu Okano
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Abstract
A chromate-treated steel strip comprising a chromate film on a zinc plated steel strip is improved in corrosion resistance and coating adherence by forming the chromate film of three layer structure consisting of a metallic Cr layer, a Cr.sup.3+ oxide layer, and an outermost surface layer of SiO.sub.2, and Cr.sup.3+ oxide plus Cr.sup.6+ oxide. The three layered chromate film is deposited on a zinc plated steel strip by effecting cathodic electrolysis in a bath containing hexavalent chromium, colloidal silica, optional alumina sol, and a fluoride, by supplying electricity at a specific current density to a controlled quantity.
Claims4
A method for preparing a chromate-treated zinc-plated steel strip, comprising
- effecting cathodic electrolysis on a zinc-plated steel strip in a bath containing 2.6 to 78 grams per liter of hexavalent chromium, 0.5 to 50 grams per liter, calculated as SiO.sub.2, of colloidal silica, and 0.05 to 5.0 grams per liter, calculated as F, of a fluoride, and substantially free of sulfate and chloride, at a current density of 1 to 50 A/dm.sup.2 and to an electricity quantity of 5 to 100 C/dm.sup.2.
A method for preparing a chromate-treated zinc-plated steel strip, comprising
- effecting cathodic electrolysis on a zinc-plated steel strip in a bath containing 2.6 to 78 grams per liter of hexavalent chromium, 0.5 to 50 grams per liter, calculated as SiO.sub.2, of colloidal silica, 0.05 to 25 grams per liter, calculated as Al.sub.2 O.sub.3, of alumina sol, and 0.05 to 5.0 grams per liter, calculated as F, of a fluoride, and substantially free of sulfate and chloride, at a current density of 1 to 50 A/dm.sup.2 and to an electricity quantity of 5 to 100 C/dm.sup.2.
A method for preparing a chromate-treated zinc-plated steel strip, comprising
- effecting cathodic electrolysis on a zinc-plated steel strip in a bath containing 2.6 to 78 grams per liter of hexavalent chromium, 0.5 to 50 grams per liter, calculated as SiO.sub.2, of colloidal silica, and 0.05 to 5.0 grams per liter, calculated as F, of a fluoride, and substantially free of sulfate and chloride, at a current density of 1 to 50 A/dm.sup.2 and to an electricity quantity of 5 to substantially less than 30 C/dm.sup.2.
A method for preparing a chromate-treated zinc-plated steel strip, comprising
- effecting cathodic electrolysis on a zinc-plated steel strip in a bath containing 2.6 to 78 grams per liter of hexavalent chromium, 0.5 to 50 grams per liter, calculated as SiO.sub.2, of colloidal silica, 0.05 to 25 grams per liter, calculated as Al.sub.2 O.sub.3, of alumina sol, and 0.05 to 5.0 grams per liter, calculated as F, of a fluoride, and substantially free of sulfate and chloride, at a current quantity density of 1 to 50 A/dm.sup.2 and to an electric of 5 to substantially less than 30 C/dm.sup.2.
Dependencies are inferred from the claim text.