Influence of freezing-thawing on atmospheric corrosion of low alloy weathering steels

Two low alloy weathering steels were exposed in three different environments which are indoor, freezing in door and outdoor to investigate the influence of freezing-thawing cycles on their initial corrosion behavior. The corrosion resistance of the tested steels was evaluated by weight loss measurements and an electrochemical method. The rust morphology and alloy elements distribution in rust layers were analyzed by scanning electron microscopy and energy dispersed spectroscopy, respectively. It was found that the environment with low temperature and humidity is favorable to form a compact rust layer, while a rust layer formed in the environment with high temperature and humidity is loose. Freezing-thawing cycles produce cracks in a loose rust layer. The reason is that there is much liquid water in pores in a loose rust layer; when the liquid water transits solid phase, the water will produce a greater stress resulting in cracks in the rust layer. However, there is not liquid water in a compact rust layer; the influence of freezing-thawing cycles on a compact rust layer is negligible.