Multi-method assessment of atmospheric corrosion for three railway steels in southwest humid subtropical climates

Southwestern China features a subtropical monsoon humid climate that induces severe corrosion of railway infrastructure, yet long-term field data and systematic material evaluation for railway steels remain scarce in this region. This work established a multi-method validation system integrating 365-day field online monitoring, 365-day natural exposure, and 96- h indoor accelerated cyclic immersion testing, to systematically investigate the atmospheric corrosion behaviour of U71Mn, U75 V, and Q500NH steels in the subtropical humid climate of China. The three steels exhibit distinct seasonal fluctuations in corrosion rate. Their annual average corrosion rates measured by online monitoring and 12-month natural exposure test are 5.13–6.00 μm/a and 6.36–8.55 μm/a, respectively, both classified as mild–moderate corrosion. Q500NH weathering steel exhibits a 23%–25.6% lower corrosion rate than the two rail steels, and temperature is identified as the dominant environmental factor. This study provides field-based data support and engineering guidance for material selection and corrosion protection of railway infrastructure in subtropical humid regions.