Electrochemical Study of the AISI 409 Ferritic Stainless Steel: Passive Film Stability and Pitting Nucleation and Growth

The aim of the present work was to study the passive film stability and pitting corrosion behavior of the AISI 409 stainless steel. The electrochemical tests were carried out in 0.1 M NaCl solution at room temperature. The general electrochemical behavior was assessed using electrochemical impedance spectroscopy (EIS) measurements whereas the semiconducting properties of the passive film were evaluated by the Mott-Schottky approach. Pitting corrosion was investigated using potentiodynamic and potentiostatic polarization tests. Surface morphology was examined using confocal laser scanning microscopy and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the composition of precipitates that could act as preferential sites for the onset of pitting corrosion. The results showed that the passive film presents n-type semiconductive behavior. Grain boundaries played an important role as pitting initiation sites for the AISI 409 stainless steel.本研究旨在探究AISI 409不锈钢的钝化膜稳定性与点蚀行为。电化学测试于室温下的0.1 mol/L氯化钠溶液中开展。整体电化学行为通过电化学阻抗谱（electrochemical impedance spectroscopy, EIS）测试进行评估，而钝化膜的半导体特性则采用莫特-肖特基（Mott-Schottky）方法表征。点蚀腐蚀的研究采用动电位与恒电位极化测试完成。表面形貌借助共聚焦激光扫描显微镜与扫描电子显微镜（scanning electron microscopy, SEM）进行观测。通过能量色散X射线能谱（energy dispersive X-ray spectroscopy, EDS）分析，以鉴定可能作为点蚀起始优先位点的析出相成分。结果表明，该钝化膜呈现n型半导体行为。晶界作为AISI 409不锈钢的点蚀引发位点发挥了重要作用。