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利用扫描电镜对X70管线钢焊接接头微观结构进行了观察,采用中性5%连续盐雾试验考察了其焊接接头表面的腐蚀性能,分析了X70管线钢焊接接头在盐雾介质中腐蚀行为,对点蚀坑内腐蚀产物进行EDS分析,探讨了X70管线钢焊接接头表面点蚀机理。结果表明,X70管线钢焊接接头在盐雾环境中耐蚀性低,容易诱发局部点蚀,Cl-对X70管线钢焊接接头的腐蚀起主导作用;其腐蚀过程主要由表面点蚀、形成腐蚀产物层、裸露的焊接接头表面腐蚀等3个部分组成,其中点蚀是裂纹萌生和扩展的主要来源;腐蚀产物主要是由Fe的氧化物和少量Fe的氯化物构成,其形成的氧化膜提高了其防盐雾腐蚀能力。
The microstructure of welded joint of X70 pipeline steel was observed by scanning electron microscope. The corrosion performance of welded joint of X70 pipeline steel was investigated by neutral salt spray test with 5% neutral salt spray. The corrosion behavior of X70 pipeline welded joint in salt spray medium was analyzed. The corrosion products in pitting pits were analyzed by EDS, and the pitting corrosion mechanism on the surface of welded joint of X70 pipeline steel was discussed. The results show that the corrosion resistance of X70 pipeline steel welded joint is low, which is easy to induce local pitting. The corrosion resistance of X70 pipeline steel is dominated by the surface pitting corrosion and the formation of corrosion products Layer, the exposed surface of the welded joint corrosion and other three parts, of which pitting corrosion is the main source of crack initiation and expansion; corrosion products mainly composed of Fe oxide and a small amount of Fe chloride, the formation of the oxide film increased Its salt spray corrosion resistance.