Applications, Mechanisms, and Key Technical Challenges of Rare Earth Elements in Weathering Steels

Weathering steels have been widely used in transportation, energy facilities, and civil infrastructure because of their good atmospheric corrosion resistance and long service life. Their corrosion resistance is generally achieved by adding alloying elements such as Cu, P, Cr, and Ni, which promote the formation of a stable and protective rust layer. Among these elements, however, Ni and Cr are relatively expensive and their resources are limited. Therefore, reducing the use of Ni and Cr while maintaining good corrosion resistance has become an important issue in the development of weathering steels. Recent studies have demonstrated that rare-earth elements can markedly improve the corrosion resistance of steels through multiple mechanisms, including optimization of rust-layer structure, microstructural refinement, inclusion modification, and regulation of grain-boundary characteristics. Rare-earth microalloying therefore provides an effective approach to reducing the consumption of conventional alloying elements in weathering steels. This paper systematically reviews the corrosion mechanisms of weathering steels, the evolution of rust-layer structures, and the roles of alloying elements, with particular emphasis on the effects of Cu, P, Cr, and Ni on the densification and stabilization of rust layers. The microalloying effects of rare-earth elements, their inclusion-modification behavior, and their deoxidation and desulfurization mechanisms are also summarized, and their roles in reducing pitting susceptibility and promoting the formation of stable protective rust layers are clarified. In addition, the occurrence states of rare-earth elements in steel and their effects on performance stability are discussed. Key challenges encountered in the industrial application of rare-earth steels, including fluctuations in rare-earth yield and continuous-casting nozzle clogging, are also summarized. The available evidence indicates that the effective application of rare-earth elements in weathering steels remains constrained by molten-steel cleanliness, inclusion control, and the stability of continuous-casting operations. Future research should focus on technologies for the stable addition and controlled occurrence of rare-earth elements under low-oxygen and low-sulfur smelting conditions, thereby enabling the efficient utilization and stable industrial application of abundant rare-earth resources in weathering steels.