Corrosion Behavior of ZG20Mn Exposed to Atmosphere of Qingdao Bay Bridge

Exposure test was carried out on ZG20Mn steel in the atmosphere of Qingdao Bay Bridge for 7 a. The corrosion behavior of ZG20Mn steel was studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that in the atmosphere of Qingdao Bay Bridge, with the increase of exposure time, the corrosion rate showed a downward trend. The relationship between average corrosion depth and exposure time conformed to a power function. With the increase of exposure time, the tendency of localized corrosion of ZG20Mn steel increased, and the depth of pitting corrosion increased. MnS inclusions and chlorinated salt particles promoted the occurrence of corrosion. The corrosion products of ZG20Mn steel exposed to the atmosphere of Qingdao Bay Bridge for 7 a were mainly composed of α-FeOOH, α-Fe₂O₃ and Fe₃O₄. The continuous generation and deposition of α-FeOOH was the main reason for the gradual decrease of corrosion rate of steel in atmosphere. The presence of Fe₃O₄ indicated that the corrosion products with electro-chemical activity participated in the cathodic depolarization process.