Hot-dip Galvanizing of Carbon Steel after Cold Rolling with Oxide Scale and Hydrogen Descaling

A new processing method for producing hot-dip galvanized steel is designed and tested, in which pickling is skipped. Hot-rolled low carbon steel sheets are rolled with oxide scale in an experimental mill at room temperature, prior to annealing under a 20% hydrogen reducing atmosphere and galvanizing on a hot-dip galvanizing simulator. Micro-cracks formed in the oxide scale during cold rolling roughen the steel surface and enlarge the specific surface. Through-thickness cracks provide transport channels for hydrogen, and hence the reduction of oxide scale is enhanced. When the sheet is dipped in the zinc bath, cracks are submerged by liquated zinc and the defects are not distinct after hot-dip galvanizing. The overlay coating occludes with rough surface of the sheet, whereby a superior coating adherence is realized.