Effect of Heat Treatment on Corrosion Behavior of S275 Mild Steel Using Accelerated DC Voltage, LPR, and EIS

Abstract This study used an external DC voltage of 1.5 V to accelerate corrosion in heat-treated S275 mild steel samples at different time intervals. LPR and EIS were used to study the corrosion behavior of original and quenched steel samples. There was only a negligible difference in the corrosion rate (CR) for the original and the quenched samples up to 30 min of voltage application in a 3.5% NaCl electrolyte media. When the exposure time increased to 60 min, the original sample showed seven times higher CR than the quenched samples. The pits on the surface of the original samples acted as cathodes, enhancing the reaction rate on the surface and increasing its CR dramatically. This led to bimodal corrosion, where the first part is led by concentration and diffusion; while, the second part is led by localized corrosion. The smaller pits on the original surface samples served as cathodic reaction centers, exacerbating corrosion. The corrosion rate of the original samples ranged from 0.8 to 7.8 mmpy; whereas, the corrosion rate of the quenched samples remained consistently around 0.8 mmpy. This trend can be observed in long-term corrosion in different metals. The uniformly oriented martensitic microstructure and the quenched samples’ small grain size prevented the enhanced ion penetration due to applied voltage. This study analyses the long-term stability of structural steel samples in marine environments by accelerating the corrosion rate by an applied external DC voltage.