Corrosion Behavior of Typical Engineering Structural Steels in a Plateau Valley Atmospheric Environment

This study systematically investigated the corrosion behavior of three typical engineering structural steels (Q235, Q420, and Q420qENH) in the plateau valley atmospheric environment of the Sichuan-Tibet region using field exposure tests (including uniform corrosion and stress corrosion coupon tests), electrochemical measurements, and microscopic characterization. The results reveal that the three steels underwent predominantly uniform corrosion, accompanied by pitting corrosion, regardless of the presence of stress. Compared with Q235 and Q420 steels, Q420qENH exhibits superior corrosion resistance, which is ascribed to the denser rust layer formed as a result of its corrosion-resistant composition. Under tensile stress, both the uniform corrosion rate and pit dimensions increased significantly relative to stress-free conditions, demonstrating a pronounced accelerating effect of stress on uniform and localized corrosion. Furthermore, the enrichment of sulfur within the rust layer at the pit bottoms suggests the involvement of atmospheric SO₂ in the localized corrosion process, which aggravates the breakdown of the rust layer and the acidification of the local environment at the pit bottom, thereby promoting pit growth.