工业海洋大气环境下焊接耐候钢Q355NHD腐蚀后力学性能研究

随着钢结构桥梁建设需求不断提高、应用日益广泛,耐候钢以其优良的耐候性能,从材料层面为钢桥防腐提供了一种理想方案;但是,由于中国应用耐候钢的时间较短,耐候钢在某些自然环境下的适用性尚未得到充分论证,对其腐蚀后基本力学性能和疲劳性能的认识尚不完善。为此,以钢桥常用的Q355NHD焊接耐候钢及其对接焊缝为研究对象,针对中国滨海城市常见的工业海洋大气环境,通过周期浸润加速腐蚀试验探讨Q355NHD的耐候性能,并对腐蚀后Q355NHD的单调拉伸性能和疲劳性能开展试验研究。基于形貌观察、基体扫描、锈层分析和腐蚀深度计算等多角度分析,发现在模拟工业海洋大气环境下,Q355NHD尽管会形成具有一定致密性的锈层,但其腐蚀速率等宏观指标相比于普通钢并不突出。腐蚀后单调拉伸试验结果表明:腐蚀8周(等效于青岛受工业污染的海洋大气环境下自然腐蚀20年)后Q355NHD母材试件的屈服强度和抗拉强度分别下降8.1%和7.2%,对接焊缝试件的屈服强度和抗拉强度分别下降14.1%和12.5%。腐蚀后疲劳试验结果表明:腐蚀8周后Q355NHD母材试件和对接焊缝试件的设计疲劳强度分别下降35.6%和30.3%,为317.9 MPa和211.0 MPa,但仍然满足《钢结构设计标准》(GB 50017-2017)中相应构造类别的疲劳设计要求。经与既有文献报道的Q355普通钢试验结果对比,表明尽管Q355NHD在工业海洋大气环境中未表现出良好的耐腐蚀性能,不建议按免涂装使用,但其力学性能在不同批次试验结果中处于较高水平,可以视为一种优质的Q355钢材。

Study on the Mechanical Properties of Weathering Steel Q355NHD After Corrosion in an Industrial Marine Atmospheric Environment

With the increasing demand for and application of steel bridge construction, weathering steel provides an ideal scheme for steel bridge corrosion prevention due to its excellent weatherability. However, due to the short application time of weathering steel in China, the applicability of weathering steel in some natural environments has not been fully demonstrated, and its basic mechanical properties and fatigue properties after corrosion have not been completely understood. In this study, Q355NHD weathering steel and its butt welds, which were commonly used in steel bridges, were taken as the research objects. The weathering resistance of Q355NHD was investigated using periodic immersion corrosion tests in a typical industrial marine atmospheric environment for a coastal city in China, and the monotonic tensile and fatigue properties of Q355NHD after corrosion were studied. Based on the multi-angle analysis including morphology observation, matrix scanning, rust layer analysis, and corrosion depth calculation, it was found that a slightly dense rust layer was formed on the surface of Q355NHD under the industrial marine atmosphere. However, its corrosion rate and other macro corrosion-related indicators were not different from those of the ordinary Grade Q355 steel. The results of the monotonic tensile tests after corrosion showed that the yield strength and tensile strength of the Q355NHD base metal specimens decreased by 8.1% and 7.2% respectively after 8 weeks of corrosion (equivalent to 20 years of natural corrosion in the Qingdao industrial marine atmosphere), and the yield strength and tensile strength of the butt weld specimens decreased by 14.1% and 12.5% respectively. The fatigue test results showed that the design fatigue strength based on two million loading cycles of the Q355NHD base metal and butt weld specimens decreased by 35.6% and 30.3% to 317.9 MPa and 211.0 MPa respectively after 8 weeks of corrosion, but still met the fatigue design requirements of the corresponding structural categories in GB 50017-2017. However, Q355NHD did not show a better corrosion resistance in the industrial marine atmospheric environment compared with the ordinary Q355 steel test results reported in existing literature, and was not recommended for use without coating. Moreover, its mechanical properties were at a high level in different batches of test results, and it can therefore be regarded as a high-quality Q355 steel. The improvement in the corrosion resistance and applicability in different corrosion environments in practical engineering need to be further studied in the future.