Influence of white rust on sheets subjected to the continuous hot-dip galvanizing process

Abstract

Zinc-galvanized steels are widely used in industries as they offer good results from a cost-benefit perspective, as well as possessing the required chemical/physical properties. Whitish stains on the surface of zinc-galvanized steels are occasionally observed in industrial processes even before their final application – known as white rust. Besides the compromised aesthetic appearance, it is often difficult to adopt protective preventive measures to avoid this pathology. Furthermore, the evident reduction in costs due to industrial competitiveness leads to a decrease in the protective zinc layer or a shorter galvanizing time. A study was conducted to evaluate the variation in mechanical resistance related to the degree of oxidation/corrosion in the continuous hot-dip galvanizing process. Thus, through mechanical tests, the possible change in the material's resistance was analyzed with samples containing different stages of white rust. The mechanical characterization was performed via a tensile test. Due to the fact that the white rust did not present an advanced stage of corrosion, no significant variations in mechanical resistance were observed in the tested specimens. However, the sample with the highest rate of white rust showed a greater deformation index and a lower maximum stress value. When compared to an SAE 1015 steel, the hot-dip galvanized material has inferior mechanical properties, which may be due to the fact that the zinc bath has a temperature of 450°C, influencing the results.