Tin-free steel strips useful in the manufacture of welded cans and process for making

摘要

A tin-free steel strip comprising a steel strip, 40 to 150 mg/m2 of a metallic chromium layer on the steel surface, and 5 to 25 mg/m2 of a chromium compound containing layer thereon wherein the metallic chromium layer contains a plurality of protrusions, exhibits improved corrosion resistance and weldability and is thus useful in the manufacture of welded cans. Preferably, 1x1011 to 1x1014 protrusions having a diameter of 5 to 1000 nm at the base thereof are present per square meter of the metallic chromium layer surface. The tin-free steel strip is produced by chromium plating a steel strip in an aqueous solution containing CR6+ preferably to a weight of 40 to 140 mg/m2, subjecting the chromium plated strip to anodic electrolysis, preferably at an eectricity quantity of 0.1 to 10 C/dm2, and subjecting the strip to a cathodic treatment in an aqueous solution containing Cr6+ and a chromium plating aid so as to deposit additional metallic chromium, preferably in a weight of 10 to 60 mg/m2.