Abstract: In a conventional electrolytic chromating bath, a steel sheet is subjected to a cathodic electrolytic chromate treatment at a relatively high speed of 400 to 1,000m per minute, to form simultaneously a lower layer of metallic chromium and an upper layer of hydrated chromium oxides on the surface of said steel sheet; and then, said electrolytically chromated steel sheet is subjected to an anodic electrolytic treatment under the following conditions in said electrolytic chromating bath, to adjust the amount of said hydrated chromium oxide layer within the range from 0.1 to 0.3mg/dm.sup.2 :Bath temperature: room temp. -- 70.degree. C;Anodic current density: 0.5 - 8 A/dm.sup.2, preferably 0.5 - 4 A/dm.sup.2 ;Treating time: 0.5 - 2 sec;Amount of electricity: 1 - 8 Coulomb/dm.sup.2.

Abstract: Method of electrolytically post-treating an electrolytically chromate treated or metallic chromium plated steel sheet comprises anodically treating the said electrolytically chromate threated or metallic chromium plated steel sheet in an electrolyte other than an aqueous solution easily dissolving metallic chromium. The anodically treated steel sheet can be treated cathodically in an electrolyte with the said anodically treated steel sheet being employed as the cathode.