The high surface quality and strong anticorrosion performance of galvanized steel sheet favor its widespread use in many industries such as construction, home appliance, automotive, and shipbuilding. The traditional production process of hot galvanized sheet can include hot rolling, pickling, cold rolling, cleaning, reduction annealing, and hotdip galvanizing. Pickling is an important process in the preparation of raw plate for hot-dip galvanizing, and concentrated mineral acids (e.g., hydrochloric [HCl] and sulfuric acids) are typically used to remove oxide scale on the surface of hot rolled steel strip. However, this process also results in consumption of the steel material, while over-and under-pickling can give rise to surface defects. In addition, emissions of HCl, a hazardous air pollutant, and the discharge of waste acid are of increasing environmental concern worldwide, particularly in those developing economies that have boosted steel production capacity. To overcome these issues, several acid-free (physical) descaling methods have been developed for oxide scale removal such as iron particle friction, plasma descaling, shot peening, grinding roller scrubbing, and spraying. [1][2][3] In the current economic climate, the steel industry faces major challenges to develop new and efficient green production technologies while realizing sustainable development.A typical pickling-free galvanized sheet production process comprises three main stages, i.e., hot rolling, reduction annealing, and hot-dip galvanizing. The hot rolling stage requires careful control to obtain oxide scale with a structure and thickness that is suitable for direct reduction. The oxide scale can then be reduced to pure iron in a reducing atmosphere, thus ensuring good wettability of the substrate for the continuous galvanizing processes. Hence, the shortcomings of pickling, and skip plating defects caused by the selective oxidation of alloyed elements like Si and Mn, are avoided. Waste acid emissions (equivalent to 20 kg per ton of steel) are also eliminated, and the overall production efficiency is much improved.The control of oxide scale on hot rolled steel strip during the pickling-free reduction galvanization process has been studied in detail. The oxide scale formed on iron during heating consists of three layers: the outermost layer is Fe 2 O 3 ; the middle layer comprises Fe 3 O 4 ; and the inner layer closest to the substrate is Fe 1 À y O. Between 570 and 1371 °C, the Fe 1 À y O phase is stable. As temperatures drop below 570 °C, Fe 1 À y O becomes unstable and transforms into a mixture of α-Fe and Fe 3 O 4 . According to the microstructure transformation mechanism of oxide scale, it