Effect of heat treatment on the passivity and corrosion resistance of steel rebar in simulated cement pore solutions

This study investigated the effects of isothermal annealing in the range 400–650°C and quench and tempering (Q&T) at 300°C and 400°C on the corrosion resistance of steel rebars immersed in simulated concrete pore solution (CPS) with and without chloride. Various electrochemical techniques were used to characterize the heat-treated rebars' general and localized corrosion behavior in both environments. Electrochemical impedance spectroscopy (EIS) results revealed that the passive film resistances of Q&T rebars were higher than the annealed samples in a chloride-free CPS. Testing in chloride-containing CPS resulted in marked degradation of the film properties for all heat-treated rebars. EIS and anodic potentiodynamic polarization curves of rebars tested in chloride-containing CPS indicated that the passive film resistance and the pitting potential improved with increasing the tempering temperature from 300°C to 400°C. X-ray photoelectron spectroscopy (XPS) analysis of the composition of the passive film developed in pure CPS for rebars Q&T 400°C, Q&T 300°C, and annealed at 400°C suggested a correlation between enhanced corrosion resistance and a higher Fe²⁺/Fe³⁺ ratio.