ULTRASMOOTH: A Two–Side Hot–Dip Galvanized Steel for Exposed Automotive Applications

Armco's process for finishing a continuous hot-dip zinc coating on steel to achieve a surface finish comparable to that of cold-rolled steel is described. The process excludes oxygen from the jet nozzle finishing operation by enclosing the jet nozzles and strip within a chamber and supplying high purity nitrogen as the wiping media to the jet nozzles. After leaving the coating chamber, the strip passes through a steam mist which minimizes the spangle formation. All grades of ULTRASMOOTH are temper rolled to meet the surface texture requirements characteristic of automotive Class 1 cold rolled steel. The coated surface is free of ripples, dross and oxide patches. Coating uniformity is excellent. The spot welding characteristics are the same as other continuously hot-dip galvanized steels. The consistency and uniform reactivity of the coating surface results in even deposition of chemical pretreatments and uniform paint adherence. Mechanical properties, formability and automotive applications for each ULTRASMOOTH base metal grade are described.