采用腐蚀失重法、宏观形貌观察法、SEM、XRD、电化学及拉伸实验等分析手段对Q235和Q450NQR1在南沙大气环境中暴晒21和34个月后的腐蚀行为进行研究。结果表明，2种钢在南沙海洋大气环境中腐蚀动力学过程分为2个阶段，第二阶段腐蚀速率较第一阶段小。耐候钢Q450NQR1在短期内就已体现出更好的耐蚀性。暴晒21和34个月后，Q235朝天面和朝地面的锈层均比Q450NQR1的厚，且锈层中的裂纹更多，利于O₂和Cl^-向基体扩散，加速腐蚀过程。2种碳钢朝天面和朝地面锈层的主要成分组成为γ-FeOOH、α-FeOOH、β-FeOOH和Fe₃O₄，各产物的相对含量随着暴晒时间的延长都有一定的差异。此外，2种钢的朝地面均比朝天面的腐蚀严重，这是由于朝地面的锈层极易脱落，使其对腐蚀介质的阻碍作用减弱。随着暴晒时间的延长，碳钢Q235和耐候钢Q450NQR1表面锈层不断增加，抗拉强度逐渐降低。即在使用过程中随着锈层的增厚，Q235和Q450NQR1钢越容易失效，引发安全事故。

Many countries have begun to focus on the development and utilization of marine resources, involving ports, docks, oil production platforms, cross-sea bridges, large ships, and other marine engineering facilities, since beginning of the 21st century. Marine atmospheric corrosion issues encountered during construction put the safety of these marine engineering facilities in jeopardy. The Nansha Islands, which are located in the southernmost part of the South China Sea, are in a typical tropical marine atmosphere environment with no long-term corrosion data. The steel used in marine engineering is the premise of expanding marine space and exploiting marine resources, as well as the guarantee of enhancing marine national defense strength and safeguarding maritime rights and interests. Because of its poor corrosion resistance, the service life has certain limitations. As a result, studying the corrosion mechanism of carbon steel in this typical atmospheric environment after long-term exposure is crucial for engineers. The corrosion behavior of low carbon steel Q235 and weathering steel Q450NQR1 was investigated using the corrosion loss method, macroscopic morphology observation, SEM, XRD, and electrochemical and tensile tests after 34 months of exposure in the Nansha atmospheric environment. The results show that the corrosion dynamic of the two sheets of steel in the marine atmosphere of Nansha Islands can be divided into two stages. The corrosion rate of the second stage is smaller than that of the first stage. Weathering steel Q450NQR1 has demonstrated better corrosion resistance in a short exposure time. The rust layer on the skyward and field-ward sides of mild steel Q235 is thicker than that of weathering steel Q450NQR1 after 21 and 34 months of exposure, and there are more cracks in the rust layer, which could promote oxygen and chloridion diffusion to the substrate and speed up the corrosion process. The main components of corrosion products are γ-FeOOH, α-FeOOH, β-FeOOH, and Fe₃O₄, the relative contents of each product were different with the extension of exposure time. Furthermore, corrosion on the field-ward sides of the two steel sheets was worse than corrosion on the skyward sides. This is because the rust layer on the field-ward side was easily removed, resulting in a weakened resistance to corrosive medium. With the extension of exposure time, the thickness of the rust layer on the skyward side of carbon steel Q235 and weathering steel Q450NQR1 is increasing, and the tensile strength was gradually reduced. That is, Q235 and Q450NQR1 are more likely to fail owing to the thickening of the rust layer during use resulting in safety accidents.