南海大气环境下304不锈钢的点蚀特性研究

Pitting Characteristics of 304 Stainless Steel in the Atmospheric Environment of the South China Sea

目的研究南海大气环境中服役的304不锈钢的点蚀原因与机理。方法以不同暴露周期的304不锈钢试样为研究对象,采用动电位极化、电化学交流阻抗谱、扫描电镜和Kelvin探针技术对其进行分析研究。结果随着暴露时间的延长,304不锈钢表面的点蚀坑数量和深度均逐渐增加,其极化曲线中,钝化区间缩短,点蚀电位负移,阳极极化曲线斜率明显减小,并出现反复再钝化现象,钝化曲线逐渐消失,同时阻抗测试中的膜层电阻越来越小。SEM分析表明,304不锈钢暴露初期出现不连续的点蚀,点蚀坑向纵深发展,暴露后期出现点蚀群,局部有多个点蚀坑连成一片形成溃疡状的腐蚀表面,同时随暴露时间的延长,扫描试样微区的Kelvin表面电位不均匀性逐渐增强。结论 304不锈钢试样的耐蚀能力随暴露时间的增加而不断下降,点蚀现象不断增加。暴露初期,点蚀坑主要向纵深发展;暴露后期,点蚀坑的宽度达到一定程度后,本体溶液向坑内迁移,稀释了坑内溶液的酸度,点蚀坑向纵深和横向同时发展。

The work aims to study the pitting corrosion causes and mechanism of 304 stainless steel in atmospheric environment of the south China sea.Potentiodynamic polarization,electrochemical impedance spectroscopy,scanning electron microscopy and Kelvin probe technology were used to analyze and investigate 304 stainless steel exposed for different periods in the atmospheric environment of the south China sea.With the extension of exposure time,the number and depth of pitting pit on 304 stainless steel surface gradually increased,the passivation interval was shortened,the pitting potential moved negatively,the slope of the anode polarization curve was obviously reduced,and passivation phenomenon appeared repeatedly.Passivation curve gradually disappeared and the resistance of the membrane layer in the impedance test became smaller and smaller.SEM indicated that 304 stainless steel showed discontinuous pitting at early exposure,pitting pits developed deeper and deeper,and pitting groups appeared at late exposure.At local part,multiple pitting pits were linked together to form ulcer-like corrosion surfaces.With exposure time increased,the surface potential unevenness of Kelvin in the scanning sample was gradually enhanced.The corrosion resistance of 304 stainless steel samples decreases with the increase of exposure time and the pitting phenomena increases continuously.Pitting pits mainly develop in depth at the beginning of exposure.At the later stage of exposure,after the width of the pitting pit reaches a certain level,the bulk solution migrates into the pit and dilutes the acidity of the solution in the pit,so the pitting pit develops simultaneously in longitudinal and lateral direction.