Insights into the field corrosion behaviour of a weathering steel in Southwest China

In southwestern China, many engineering projects are in sparsely populated areas, far from industrial and marine environments. These areas are usually near fresh water, with low pollution and high humidity. However, limited research exists on the prolonged field corrosion behaviour of weathering steels in such environments, especially for weathering steels with higher strength. In this research, we conducted the field corrosion test of a weathering steel for up to 20 months in southwestern China. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), atomic force microscopy (AFM), and Raman spectroscopy were used to thoroughly characterize the rust layers in the same position. This study aims to clarify whether protective rust layers can form in this environment and to explore the structure of the rust layer at different stages. It found that formed complete rust layers effectively hinder the corrosion process, in addition, Cr enrichment was identified during early corrosion stages, preceding α-FeOOH formation and occurring independently. Cu enrichment was observed at later stages but had subtle impact on the electrochemical corrosion resistance of the inner rust layer. Combined with various types of data, a detailed corrosion mechanism is summarised. In addition, differences in corrosion rates between the skyward and groundward sides have been observed, with the evaporation rate of dewdrops identified as a key contributing factor. This study provides critical insights into the corrosion mechanisms of high-strength weathering steels in mild atmospheric environments, offering a theoretical foundation for optimizing material design and enhancing their practical application in sustainable infrastructure development.