pH值对X80管线钢热丝TIG焊接头在NaCl溶液中腐蚀行为的影响

Effects of p H Values on Corrosion Property of Hot-wire TIG Welded Joints of X80 Pipeline Steel in NaCl Solution

采用直径准1.2 mm的ER70S-3焊丝对X80管线钢进行热丝TIG焊接,利用金相显微镜分析焊接接头微观组织;采用质量损失法和电化学测试方法研究了X80管线钢母材、热丝TIG焊缝及热影响区在不同pH值NaCl溶液中的腐蚀行为。结果表明,焊缝区经过pH6.5 NaCl溶液腐蚀后的腐蚀产物最多,经PH9的碱性NaCl溶液后的腐蚀产物最少,经pH8的NaCl溶液后的腐蚀产物居中。试样经去离子水清洗后,pH6.5溶液浸泡后的焊缝表面有点蚀坑存在;pH8和pH 9溶液浸泡后焊缝表面没有发现裂纹和点蚀坑。X80管线钢接头各区域在pH6.5溶液中的腐蚀电流密度最大;在同一种溶液中,母材的腐蚀电流密度最小,热影响区的腐蚀电流密度最大,而焊缝的居中。相同浸泡时间下,热影响区的腐蚀程度高于母材和焊缝,这是由于热影响区存在晶粒粗大和大量非平衡组织的粒状贝氏体造成的。

The X80 pipeline steel was welded using hot-wire TIG welding procedure and ER70S-3 welding wire with diameter of 1.2 mm.The microstructure of the welded joint was observed by optical microscope(OM).The corrosion performances of base metal,hot-wire TIG weld zone and heat affected zone were studied using the corrosion weight loss and electrochemical testing methods.The results show that the corrosion products of the weld zone are the most in pH6.5 NaCl solution.Corrosion products of the weld zone in pH9 NaCl solution are the least.Corrosion products of the weld zone in p H8 NaCl solution are in middle.After all specimens are cleaned by deionized water,the pits are founded on the surface of the weld zone in pH6.5 NaCl solution.No cracks and pits are found on the weld surface in pH 8 and pH 9 NaCl solution.The corrosion current density of each zone of X80 pipeline steel joint in pH6.5 solution is the highest.In the same solution,the corrosion current density of base metal is the smallest,the corrosion current density of heat affected zone is the largest,and the welding seam is in the middle.At the same soaking time,the corrosion degree of HAZ is higher than that of base metal and weld,which is due to the existence of coarse grains and a large number of non-equilibrium granular bainites in HAZ.