###### Abstract  
The corrosion mechanism and characteristics of steel in typical atmospheric environments directly affect the rationality of corrosion protection methods. This study investigates the corrosion evolution law of Q235 steel that has been exposed to the urban industrial atmosphere for seven years. The mass loss is used for corrosion dynamics analysis. The rust layers have been characterized by SEM, EDS, and XRD. Finally, the corrosion mechanism was analyzed through a combination of electrochemical methods, corrosion kinetics, and rust layer characteristics. The mass loss results indicate that a two-stage corrosion power function law can still effectively describe the corrosion rate of a seven-year exposure that complies with the power function law. The short-term corrosion results fail to fully reflect the corrosion performance of Q235 steel. The typical morphological structures of \(\gamma\)-FeOOH and \(\alpha\)-FeOOH are identified, and the rust layers change from a loose and flat form to a granular and, finally, compact into a smooth surface. The crystalline phases of the rust layers include \(\alpha\)-FeOOH, \(\gamma\)-FeOOH, Fe\({}_{3}\)O\({}_{4}\)/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\). Corrosion products in the initial period are mainly \(\gamma\)-FeOOH, followed by \(\alpha\)-FeOOH, and a small amount of Fe\({}_{3}\)O\({}_{4}\)/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\). With the increase in exposure time, \(\alpha\)-FeOOH and Fe\({}_{3}\)O\({}_{4}\)/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) in the rust layer increase. SO\({}_{2}\) and Fe\({}_{3}\)O\({}_{4}\)/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) are the primary factors accelerating steel corrosion. During the first three years of atmospheric corrosion, the primary corrosion mechanism was governed by the acid cycle reaction mechanism. However, from the fifth year of atmospheric corrosion, oxygen-absorbing corrosion began to gradually dominate, specifically oxygen-absorbing corrosion. atmospheric corrosion; Q235B steel; corrosion rate; corrosion morphology; rust phases +
Footnote †: journal: Applied Sciences  
0000-0002-2300-3300]Zhejiang Southeast Space Frame Group Co., Ltd., Xiaoshan District, Yaqian Road 593, Hangzhou 311209, China 0000-0002-2300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-33000-3300-3300-3300-3300-33000-33000-3300-33000-3300-330  
for reasonable material selection and the design of anti-corrosion schemes. Such studies have important application value for reducing the rate of atmospheric corrosion of steel, extending its service life, and minimizing the various losses caused by corrosion. To date, a significant number of atmospheric corrosion studies have mainly focused on the initial stages of corrosion behaviors [8; 9; 10; 11; 12], as well as the impact of pollutants such as SO\({}_{2}\) and Cl\({}^{-}\) during short-term (0.5-3 years) atmospheric exposure [13; 14; 15; 16; 17; 18] and deposited atmospheric particulates [11] on the corrosion rate. Environmental parameters such as temperature, relative humidity [18; 19], and time-of-wetness [20; 21] were also explored to reveal their effects on corrosion rates. Some studies have established corrosion kinetic models for both short-term (3 years) and long-term (16 years) atmospheric exposures [22; 23; 24; 25; 26; 27]. Models that predict corrosion rates have also been constructed [28; 29]. In addition, the evaluation of corrosion products produced after atmospheric exposure is beneficial for understanding the corrosion behaviors of different steel materials, environmental conditions, and exposure time [30]. A number of studies have investigated the characteristics of corrosion products under short-term (a few months to a year) [31; 32; 33; 34; 35; 36] and long-term [30; 4] atmospheric exposures. The extension of the service life of steel is affected by its type and chemical composition [37].