Abstract: A zinc, zinc alloy or aluminum alloy plated steel strip having chromate coatings on both surfaces is coated with a lubricating resin composition for improving formability and corrosion resistance. In one form, a resin composition including a base resin, silica, a high-melting polyolefin wax and optionally, a low-melting polyolefin wax is applied on both surfaces for improving formability. In a second form, a resin composition including a base resin, silica, and a powder fluoro resin is applied on both surfaces for improving corrosion resistance. In a third form, the chromated steel is coated with a resin composition including a base resin, silica and a solid lubricant on one side and with a resin composition including a base resin and silica on the other side for improving both formability and corrosion resistance.

Abstract: A cold rolled steel sheet or plated steel sheet having an improved press formability as well as excellent phosphatability, resistance to galling and spot weldability is produced by controlling a surface roughness pattern of the steel sheet so as to satisfy a center-line average surface roughness of 0.3-2.0 .mu.m and a regularity parameter in at least one direction of not more than 0.25 defining the regularity of surface roughness.

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: This invention provides a tin-free steel sheet, having superior lacquer adhesion, comprising metallic chromium and chromium oxide coatings on a steel sheet, characterized in that the chromium oxide coating is controlled such that I.sub.Cr.sup.580 /(I.sub.Cr.sup.580 +I.sub.Cr.sup.660) has a value of 0.5 or more provided that I.sub.Cr.sup.580 is the percent transmission corresponding to ol linkage and I.sub.Cr.sup.660 is the percent transmission corresponding to oxo linkage in the infrared absorption spectrum of said chromium oxide coating as measured by Fourier transform infra-red spectroscopy.

Abstract: Tin-free steel sheets having improved resistance to retorting treatment are produced by chromium plating a steel sheet through cathodic electrolysis in a chromium ion-containing aqueous solution to form a metallic chromium coating, reversely electrolyzing the chromium plated steel sheet by a successive anodizing treatment in the same solution, and subjecting the sheet to an electrolytic chromate treatment in another aqueous solution of chromic acid, a chromate or dichromate. The chromium plating and reverse electrolysis should be carried out so as to satisfy the equations:x+1.ltoreq.y.ltoreq.x+41.ltoreq.x.ltoreq.6where y and x are the quantities of hydrated chromium oxides present on one surface of the steel sheet after the chromium plating step and after the reverse electrolysis step, respectively, as expressed in mg (in terms of metallic chromium) per square meter of the surface.

Abstract: Tin-free steel sheets exhibiting improved retorting resistance with respect to paint adhesion are produced by chromium plating a steel sheet through cathodic electrolysis in a chromium ion-containing solution, reversely electrolyzing the sheet by a successive anodizing treatment in said solution, and subjecting the sheet to an electrolytic treatment in an aqueous chromate solution. The SO.sub.4.sup.-- concentration of the chromate solution used in the electrolytic chromate treatment should be limited to the range of 0.01 to 0.10 gram per liter of the solution.

Abstract: A surface treatment method for tin-free steel, which comprises applying a water solution, containing a polymer obtained from one or two or more kinds of monomers of unsaturated carboxylic acids, on to the surface of a steel sheet having a metallic chromium layer formed thereon and having a film, mainly consisting of hydrated chromic oxide, formed on the above layer, and then conducting heating and drying. The coating of tin-free steel obtained by this method is excellent in adhesiveness and is most suitable for bonded cans requiring high-temperature treatment.