Effect of Residual Stress on Corrosion Sensitivity of Carbon Steel Studied by SECM

The effect of compressive residual stress on the reactivity of carbon steel in a neutral chloride solution was investigated by means of potentiodynamic polarization and local electrochemical measurement with scanning electrochemical microscope(SECM). Meanwhile, X-ray diffraction, as a nondestructive technique, was employed to determine the levels of residual stress in near-surface layers of carbon steel specimen. The results show that the residual stress existed in the specimen fell into the category of compressive residual stress which was inversely proportional to the corrosion sensitivity of carbon steel specimen. By using I^-/I₃^- couple as a redox mediator in the current feedback mode of SECM measurements, the Faradaic current on Pt tip, which was relevant to the rate of the I₃^- ion reduction, fell with the increase of compressive residual stress. The correlation between compressive residual stress and heterogeneous electron transfer rate has been proposed based on the inference of the localized electrochemical reactions occurred on the specimen surface.