| 摘要 |
Tin-free steel, consisting of an upper layer (I) of hydrated chromium oxide and a lower layer (II) of metallic Cr, is pretreated by subjecting a steel sheet before formation of (I) and (II), to an anodic treatment followed by a cathodic treatment in an acid electrolyte containing >= 1 chromate selected from chromic trioxide, alkaline metal dichromates and ammonium dichromate, after degreasing the sheet. Both treatments are at < 60oC and at a current density of 1-50 A/dm2 for 0.1-5 secs. in an acid electrolyte containing 5-50 g/l hexavalent Cr.
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