Study of the Passivation Film on S32750 Super-Duplex Stainless Steel Exposed in a Simulated Marine Atmosphere

The corrosion behavior and passivation mechanism of S32750 super-duplex stainless steel exposed in a simulated marine atmosphere were studied using electrochemical methods, XPS and SEM. Passivation and local corrosion occurred on the metal surface when S32750 SDSS was exposed in the simulated marine atmospheric environment. The passivation film is composed of two chromium-enriched layers. The outer layer is a very thin film at the metal/atmosphere interface of the specimen surface with higher chromium content, whereas the chromium in the inner layer seems a little depleted. The outer and inner layers had similar Fe components, and Fe3+ oxide/hydroxide was the primary oxide in the film. The outer layer contains CrO3, whereas the inner layer has Cr3+ as its primary oxide. Pitting occurred when exposure time exceeded 24 d, and the Cr content of the specimen decreased. Therefore, S32750 SDSS exposed for 24 d exhibited the best corrosion resistance.