目的 研究桥梁耐候钢板材及其焊接接头在模拟含 PM2.5 的西北工业大气环境中腐蚀行为的区别.方法 采用NaHSO3+SiO2的腐蚀介质进行干湿交替加速腐蚀实验,并采用腐蚀动力学、X射线衍射、扫描电镜+能谱、电化学测试等方法,分析了Q420qENH钢板材、焊缝及热影响区试样的腐蚀趋势、腐蚀类型及锈层的保护性,以及SiO2对腐蚀的影响.结果 Q420qENH板材试样初期腐蚀速率大于焊接试样,中后期2 种试样腐蚀速率逐渐下降并趋于一致.3 种试样腐蚀类型均为不均匀的全面腐蚀,外锈层均疏松易脱落,但焊缝、热影响区内锈层比板材致密且与钢基体结合紧密,锈层中Cu、Ni元素含量明显高于板材试样.3 种试样腐蚀30 d的自腐蚀电流密度由大到小的顺序为板材>焊缝>热影响区,自腐蚀电位由大到小的顺序为热影响区>焊缝>板材,焊缝及热影响区试样的锈层电阻分别为板材试样的 1.28 倍、1.68 倍.结论 PM2.5 中的主要成分 SiO2 易在缺陷处沉积,成为腐蚀产物的形核基底,促进了腐蚀产物的非均匀形核,不利于锈层的致密性.热影响区和焊缝形成锈层的保护性、耐蚀性能优于板材试样.
In this work,the corrosion behavior of Q420qENH weathering steel and its welded joints in industrial atmospheric environment containing PM2.5 was studied by dry-wet alternate accelerated corrosion test.The corrosion trend,corrosion type and rust layer protection of the plate,weld and heat affected zone samples,and the effect of SiO2 on corrosion were investigated.In the industrial atmospheric medium containing SiO2,the initial corrosion rate of Q420qENH plate sample was higher than that of the welding sample,and the corrosion rate of the two samples gradually decreased and tended to be the same in the middle and late period.During the entire corrosion process,the n values of the plates and welded samples were all less than 1,indicating that the corrosion of Q420qENH steel plates and welded samples was a deceleration process in the northwest industrial atmospheric medium environment containing PM2.5.The corrosion types were characterized by general corrosion and local corrosion,but the local corrosion pit size of the plate was large and the corrosion was serious.The outer rust layer of the three samples was loose and easy to fall off,and there were defects such as long cracks and holes.However,the rust layer in the weld and heat affected zone was denser than the plate and closely bonded to the steel matrix,and the content of Cu and Ni elements in the rust layer was significantly higher than that of the plate sample.The three samples all had obvious element enrichment phenomenon,and the Si element enrichment in the rust layer of the weld and heat affected zone samples was less than that of the plate,which indicated that the inner rust layer formed by the weld and heat affected zone samples could be more concentrated.The self-corrosion current of the three samples after corrosion for 30 days wa:plate>weld>heat affected zone,and the self-corrosion potential wa:heat affected zone>weld>plate.The rust layer resistance of the weld and heat affected zone samples was 1.28 times and 1.68 times that of the plate samples,respectively,indicating that the protection of the rust layer formed by the heat affected zone and the weld was better than that of the plate samples,and the corrosion resistance was better than that of the plate samples.This was because the microstructure of the weld and the heat affected zone was a large amount of acicular ferrite,granular bainite and lath bainite formed in the original austenite grains.The microstructure was fine and uniform and the grain boundary was weakened,which was beneficial to the improvement of corrosion resistance.In addition,the higher Cu and Ni elements in the weld could promote the transformation of γ-FeOOH to α-FeOOH,which increased the ratio of α-FeOOH/γ-FeOOH of the welded sample,improved the compactness and stability of the rust layer,and thus improved the corrosion resistance.The PM2.5 with SiO2 as the main component is easy to deposit at the defects,which becomes the nucleation substrate of the corrosion products,promotes the non-uniform nucleation of the corrosion products,and makes the rust layer develop unevenly,so it is not conducive to the compactness of the rust layer.