Abstract: The corrosion behavior of X80 pipeline steel in simulated solution of acid soil was investigated using electrochemical measurement and metalloscope. The results show that the microstructure of the base metal is acicular ferrite, the microstructure is uniform and tiny, the distribution is parallel. The microstructure of the weld joint of X80 pipeline steel is characterized by proeutectoid ferrite, acicular ferrite and pearlite, the microstructure is uneven and bigger than base metal. No active-passive transition region is found in polarization curves of both base metal and weld joint. Both corrosion potential and charge transfer resistance of weld joint is lower than the base metal, whereas corrosive current density of the weld joint is greater than the base metal, which indicates that weld joint has a greater tendency to corrosion. The diffusion index of base metal is larger in equivalent circuit, and the corrosion produce film is denser. Corrosion resistance of the weld joint of X80 pipeline steel is lower than the base metal, due to differences in microstructure.

Key words: X80 pipeline steel, Welded metal, Microstructure, Corrosion resistance

摘要： 采用电化学测试、金相显微镜观察，研究了X80管线钢及其焊缝组织在酸性模拟液中的电化学腐蚀行为。结果表明:X80管线钢母材的显微组织主要为针状铁素体，整体上看母材的组织较为均匀、细小，位向大致呈带状分布。焊缝的显微组织由先共析铁素体、针状铁素体和珠光体组成，焊缝的晶粒大小不均匀，整体上比母材组织粗大。在酸性模拟液中， X80管线钢母材和焊缝的极化曲线只有活性溶解区，无活化—钝化区。X80管线钢焊缝的自腐蚀电位低于母材的，腐蚀电流密度大于母材，电荷转移电阻小于母材，表明X80管线钢焊缝组织发生腐蚀的倾向更大。等效电路中，X80管线钢母材的弥散指数大于焊缝的，母材的腐蚀产物膜更致密。由于显微组织差异，X80管线钢焊缝的耐腐蚀性低于母材。

关键词: X80管线钢, 焊缝, 显微组织, 耐腐蚀性能