Layer-by-layer analysis of gradient corrosion behavior of ultrasonic rolling-processed 20CrMnTi steel

The gradient corrosion behavior of 20CrMnTi treated by the ultrasonic surface rolling process (USRP) was investigated by layer-by-layer analysis. As the nanostructured layer gradient changed from the surface to the interior, multiple electrochemical behaviors were studied at different depths in a neutral corrosive environment. The results showed that the corrosion resistance of the deformed layer underwent a nonmonotonic transition. Although the outer surface exhibited excellent corrosion resistance, this resistance decreased sharply and reached a minimum at a depth of 50 mu m. This study showed that the corrosion resistance at different depths was mainly influenced by the density of low-angle grain boundaries (LAGBs) rather than by the grain size. The highest LAGB density was observed at depths of 30-50 mu m, resulting in the greatest lattice distortion that induced the lowest corrosion resistance.