Influence of Hot Rolled Steel Surface Condition on Galvanizing Reaction

The hot dip galvanizing mechanism of hot rolled Al killed steel sheets with various surface conditions were investigated.It was found that various factors of steel surface conditions affected the galvanizing reaction. The appearance of Zn coatings was improved in adequate pickling time. This pickling time affected the residual scale, smudge and surface roughness. Surface roughness of hot rolled steel sheets varied with pickling time and pretreatment methods affected the galvanizing reaction. The appearance and adhesion of Zn coating became better in a small range of surface roughness. More ramarkable result was that reactivity of substrate in molten zinc depended on the pretreatment methods. Mechanical polishing and skinpass rolling of steel sheets increased the reactivity of substrate in molten zinc more than just pickling and electropolising. Increase of residual strain and stress on the steel surface by mechanical pretreatment was observed by X-ray diffraction method. It seemed that active sites such as the lattice deffects of substrate increased by mechanical pretreatments, and therefore Zn-Fe reaction increased.