不锈钢波纹管在海洋大气环境下的腐蚀失效分析

目的 研究热带海洋大气环境下06Cr19Ni10不锈钢波纹管的腐蚀失效机理。方法 对失效导管进行宏观形貌分析，确定宏观腐蚀特征。进一步对失效管段进行显微组织以及化学成分的分析。采用体式显微镜、扫描电镜(SEM)和能谱分析(EDS)开展失效管段的微观腐蚀形貌观察和腐蚀产物分析。结果 宏观来看，导管上金属网套和波纹管外面有几处轻微腐蚀，波纹管侧面腐蚀略微严重，内部没有发现腐蚀。金相组织显示，波纹管基体材料为奥氏体晶粒，在U型波纹管顶部有少量马氏体存在，波纹管基体材料化学成分符合国标要求。扫描电镜下，波纹管外表面发生了严重的点蚀，在U型波纹管的顶部和波纹间的平台均有较大的点蚀坑，U型顶部的点蚀更为严重，并且波纹管不同部位发生了明显的晶间腐蚀。点蚀坑处的EDS显示，腐蚀产物多为Fe的氧化物，坑内还发现了少量的Cl^?，并且坑内产物的Cr元素含量明显少于基体。结论 由于波纹管固溶处理不当，导致晶界间贫铬，使材料表面大部分区域产生晶间腐蚀。同时由于波纹管顶部的塑性变形诱导马氏体生成，使得该处更容易发生点蚀，而海洋大气环境中的氯离子进一步促进了这种点蚀的发生，最终导致了波纹管的腐蚀失效，U型顶端发生的点蚀是材料失效的主要原因。

Corrosion Failure of Stainless Steel Bellows in Marine Atmosphere

The work aims to study the corrosion failure mechanism of 06Cr19Ni10 stainless steel bellows in tropical marine atmosphere. The macro morphology of the failed conduit was analyzed to determine the macroscopic corrosion characteristics. The microstructure and chemical composition of the failed pipe section were further analyzed. Stereo microscope, Scanning Electron Microscope (SEM) and Electronic Differential System (EDS) were used to observe the microscopic corrosion morphology of the failed pipe section and analyze the corrosion products. From a macro point of view, the metal mesh sleeve on the pipe and the outside of the bellows were slightly corroded. The side of the bellows was corroded slightly, and no corrosion was found inside. The metallographic structure showed that the base material of the bellows was austenite grains, and there was a small amount of martensite on the top of the U-shaped bellows. The chemical composition of the base material of the bellows met the requirements of the national standard. Under the scanning electron microscope, serious pitting corrosion occurred on the outer surface of the bellows. There were large pits on the top of the U-shaped bellows and the platform between the corrugations. The pitting on the top of the U-shaped bellows was more serious. And different position of the bellow had obvious intergranular corrosion. The EDS at the pits showed that most of the corrosion products were Fe oxides, a small amount of Cl- was also found in the pits, and the Cr content of the products in the pits was significantly less than that of the matrix. Due to improper solution treatment of the bellows, the intergranular chromium is depleted, causing intergranular corrosion in most areas of the material surface. At the same time, the plastic deformation of the top of the corrugated tube induces the formation of martensite, which makes it more prone to pitting corrosion. The chloride ions in the atmosphere further promoted the occurrence of this kind of pitting corrosion, and finally led to the corrosion failure of the bellows. The pitting corrosion occurring at the top of the U-shape is the main cause of material failure.