Abstract: Tin-free steel sheets having intimately bonded metallic chromium and hydrated chromium oxide coatings thereon and possessing improved resistance to retorting treatment and improved adhesion to paint films to be applied thereon are produced by chromium plating a steel sheet in a chromium plating bath containing an assistant to deposit and form metallic chromium and hydrated chromium oxide coatings on the sheet surface, subjecting the sheet to reverse electrolysis in the same chromium plating bath to partially dissolve away the metallic chromium and hydrated chromium oxide coatings together with the assistant anions codeposited in the hydrated chromium oxide coating, rinsing the sheet with water, and thereafter subjecting the sheet to an electrolytic chromate treatment in an electrolytic chromate treating bath.

Abstract: A method of producing an aluminum or aluminum alloy coated steel sheet with the aid of powder method is disclosed. The method comprises preliminarily applying a zinc coating having a thickness of 0.01 to 0.3 .mu.m, preferably 0.03 to 0.3 .mu.m to a steel sheet surface, applying an aluminum powder to the zinc coated steel sheet and subjecting the coated steel sheet to steps of heating, rolling and heating again or steps of rolling, heating, rolling again and heating again.