Chromium accumulates only in the inner rust layer, leading to the formation of a dense and compact rust layer with improved ability for protecting the steel against the corrosive atmosphere. In addition, Cr3+ in the rust layer is coordinated with O2 and positioned in the double chains of vacant sites within the FeO3(OH)3 octahedra network in the goethite crystal, leading to improved protective performance. Chen et al. reported that rust layers on weathering steels containing more than 4 mass% Ni is cation-selective. Besides, Fe is substituted by Ni and the inverse spinel oxide, NiFe2O4, is formed, which enhances the corrosion resistance of Ni-alloying steel. As the traditional COR-TEN weathering steels contains elements Cr and Ni, and their costs are relatively high. During the 21st century, lower cost and higher performance weathering steels were developed, driven by the need to develop steels that were more resistant to the deteriorating atmosphere, particularly with the rise in SO2 (acid rain) along with chloride ion in polluted marine atmospheres.