316L不锈钢是一种耐蚀性和加工性优异的奥氏体不锈钢。在海洋环境使用过程中发现经钝化处理的316L不锈钢波纹管在短时间内出现穿孔, 而经表面黑化处理的波纹管出现缓慢的均匀腐蚀, 没有出现点蚀穿孔现象。为了弄清波纹管穿孔的原因及机理, 采用扫描电镜、数码显微镜及金相显微镜分别对黑化处理及钝化处理的不锈钢腐蚀形貌及金相组织结构进行观察。利用X射线衍射仪(XRD)和化学成分分析技术分别对腐蚀产物的相结构及不锈钢材料的成分进行分析。结果表明,酸洗后钝化膜的破裂和海水中氯离子的残留是形成点蚀穿孔的主要原因; 表面黑化之后的波纹管由于表面形成了疏松的物质, 在海水中为均匀腐蚀, 其腐蚀的速度远低于点蚀速度。

316L stainless steel is a kind of austenitic stainless steel with the characteristics of anticorrosion and easy-machining. Pits appeared on the 316L bellows with passivation treatment in a short period of time, no pits, however, were found on the 316L bellows with blacking treatment. Uniform corrosion was observed on the bellows with blacking treatment. The corrosion morphology and metallographic strecture of stainless steel with different treatments were observed using scanning electron microscope (SEM), digital microscope and optical microscope. Chemical composition analysis and X-ray diffraction (XRD) were applied to analyze the element constitution of stainless steel and the phases existing in corrosion products respectively. The results showed that pitting caused by Cl- from sea water was the main factor to rupture the passive film. Due to the loose film on the bellows with blacking treatment, uniform corrosion occured on the surface. The corrosion rate of uniform corrosion was far slower than that of pitting corrosion.