Tin free steel having an excellent weldability and its production method

摘要

Tin free steel having three layers consisting of a bottom layer of metallic chromium, a middle layer of nickel-zinc alloy containing 10 to 90 weight percent of zinc and a top layer of hydrated chromium oxide on a steel base, and a method for the continuous production of this tin free steel which comprises: (a) chromium plating a steel base to form a layer of metallic chromium and hydrated chromium oxide, (b) nickel-zinc alloy plating the chromium plated steel base by using a nickel-zinc alloy plating electrolyte sufficiently acidic to dissolve the hydrated chromium oxide and (c) forming a hydrated chromium oxide layer on the chromium plated nickel-zinc plated steel base. Instead of (b) in the above method, a cathodic treatment in an acidic solution can be carried out for the removal of hydrated chromium oxide formed during chromium plating, and thereafter nickel-zinc alloy plating can be carried out by using a known nickel-zinc alloy plating electrolyte. This tin free steel is useful for producing welded can bodies at high speed without removing the plated layer in the welded part, since it has an excellent weldability.