Duplex stainless steels have excellent corrosion resistance due to their two-phase microstructure and electrically insulating passive film. Nevertheless, hydrogen charging causes deterioration of the corrosion protection mechanisms, resulting in increased pitting susceptibility. In this study, current-sensing atomic force microscopy was used to investigate the electrical properties of the passive film formed on 2507 duplex stainless steel before hydrogen charging. Results were compared with optical images of pitting corrosion initiation after hydrogen charging and FeCl₃ exposure. Highest passive film conductivity and current density were seen at grain boundaries, indicating poor passive film development and high pitting probability. High conductivity was also observed on the passive film located at the adjacent austenite phase, alluding to favorable conditions for pitting corrosion propagation. Phases were identified by magnetic force microscopy, while pit initiation with subsequent propagation after hydrogen charging and FeCl₃ exposure was observed using optical microscopy. Pitting corrosion initiated at grain boundaries and propagated into the austenite grains. This study identified the pitting initiation and propagation mechanisms in 2507 duplex stainless steel.

双相不锈钢具有两相组织和电绝缘的钝化膜，因此具有出色的耐腐蚀性。然而，充氢会导致腐蚀防护机制变差，导致点蚀敏感性增加。在这项研究中，使用电流感应原子力显微镜研究了充氢之前在2507双相不锈钢上形成的钝化膜的电性能。将结果与充氢和FeCl ₃后点蚀开始的光学图像进行比较接触。在晶界处观察到最高的无源膜电导率和电流密度，表明无源膜的显影不良和出现点蚀的可能性较高。在位于相邻奥氏体相的钝化膜上也观察到了高电导率，这暗示了点蚀腐蚀传播的有利条件。通过磁力显微镜鉴定相，同时使用光学显微镜观察到氢注入和FeCl ₃暴露后坑的萌生以及随后的传播。点蚀开始于晶界，并传播到奥氏体晶粒中。这项研究确定了2507双相不锈钢的点蚀引发和传播机理。