耐候钢和高性能钢腐蚀后疲劳性能2019年度研究进展

State-of-the-art review of the fatigue performance of corroded weathering steel and high performance steel in 2019

免涂装耐候钢桥梁在使用过程中长期受到腐蚀作用,影响其性能的主要有均匀腐蚀和坑蚀。坑蚀能够直接导致钢材疲劳强度降低,并且疲劳细节等级越高,坑蚀对疲劳强度的削减越严重。在钢桥设计中,疲劳设计常为控制指标,需要对耐候钢和高性能钢腐蚀后的疲劳性能进行研究。针对中国耐候钢和高性能钢开展共计20个试件的腐蚀后疲劳试验,根据ISO规范对两种钢材进行中性盐雾干/湿循环腐蚀试验,盐雾采用5%的NaCl作为腐蚀溶液,其pH值为6.5,温度控制为35℃,腐蚀120个周期;针对腐蚀后的试件进行疲劳试验,并与未腐蚀试件的疲劳试验结果对比。试验结果表明,腐蚀后耐候钢和高性能钢的疲劳强度均大幅降低;不考虑保证率时,腐蚀后HPS 485W和Q345CNH钢2×106次荷载循环的疲劳强度与未腐蚀试件相比分别降低了27.8%和26.6%;考虑95%保证率,采用m=3时,分别降低了34.7%和50.1%,并且低于FAT 125要求。腐蚀作用下,两种钢材表面形成稳定锈蚀层和蚀坑,其锈蚀层具有一定强度,疲劳裂纹均萌生于表面蚀坑部位。

Uncoated weathering steel bridges expose to the long-term effect of corrosion during the service,and the main corrosion types that influence its performance are uniform corrosion and pitting corrosion.Pitting corrosion can directly reduce the fatigue strength of steels,and the higher the level of fatigue detail,the more serious the reduction of fatigue strength.Fatigue verification is usually the control index in the design of bridge structure.Thus,the post-corrosion fatigue performance of weathering steel(WS)and high performance steel(HPS)need to be investigated.This study carries out fatigue test on corroded Chinese WS Q345CNH and HPS 70W with a total of 20 specimens.Firstly,the neutral salty spraying dry/wet cyclic corrosion test is carried out for 120 cycles in 35℃according to the ISO code,in which the 5%NaCl solution with pH=6.5 is utilized.Then,the fatigue test results of corroded specimens were compared with those of uncorroded specimens.The result indicates a notable drop in the fatigue strength of corroded WS and HPS.When the guarantee rate is not considered,the fatigue strength of HPS 485W and Q345CNH steel under 2×106 load cycles after corrosion is 27.8%and 26.6%lower than that of the uncorroded specimens,respectively.Considering 95%guarantee rate,when m=3 is adopted,it reduces 34.7%and 50.1%,respectively,and is lower than the FAT 125 requirement.The test also suggests that,the stable rust layers with a certain strength are formed on the surface of both kinds of steel.In addition,the whole fatigue cracks are initiated from the pitting flaws.