Investigation of kinetics of passive layer formation on various microstructures in thermo-mechanically treated steel in simulated concrete pore solution

Carbon steel bars are critical in steel-reinforced concrete structures, and their corrosion can lead to significant deterioration. This research explored the passive layer formation on different carbon steel microstructures using a high throughput approach. Thermomechanically treated steel bars with three distinct microstructures, i.e., martensite in the outer layer, bainite in the middle, and pearlite in the center, were vertically cut and immersed in the simulated concrete pore solution. Scanning electrochemical microscopy was employed to study the formation of the passive layer, the kinetics of the passivation, and the effective rate constant of the species inside the solution on each microstructure. Results showed that the formation of the passive layer is a time-dependent process, and passivation was influenced by the local microstructure. Martensite demonstrated superior passivation behavior compared to pearlite and bainite.