PURPOSE: To enable the execution of iron electroplating on galvannealing with a high electrodeposition efficiency by using a sulfuric acidic iron plating liquid contg. a glycol deriv. compd.
CONSTITUTION: The galvannealed steel sheet is subjected to iron electroplating by using an insoluble anode in a sulfuric acidic iron plating bath contg. 0.0001 to 0.1mol/l at least one kind of glycol deriv. compds. of ≤1000 mol.wt. selected from a polyethylene glycol deriv. and polypropylene glycol deriv. The conditions of this plating are ≥100A/dm2 current density and ≤1m/sec flow velocity of the plating liquid in the sulfuric acidic iron plating bath kept at 30 to 70°C plating bath temp. The plating bath is preferably an Fe-Zn sulfate system of ≥70g/l Fe2+ and below the threshold of ion concn., ≤0.1 Zn2+/Fe2+ weight ratio of the plating metal ions, <7g/l Fe3+ concn. and 1.8 to 2.2 pH.
KYONO KAZUAKI
YASUDA AKIRA
YAMATO KOJI
