The corrosion of gray cast iron brake discs in aggressive environments is a growing concern for the automotive industry, particularly in hybrid and electric vehicles, where reduced brake usage promotes corrosion-related degradation. This phenomenon not only affects brake performance and service life but also contributes to particulate matter emissions with potential environmental and health impacts. The present study evaluated the influence of three preconditioning materials (metallurgical graphite, electrode graphite, and metallurgical coke) on the microstructure and corrosion resistance of gray cast iron. Three independent heats were produced under identical melting conditions at 1450 °C, using each preconditioning material separately. Three specimens were obtained from each heat for microstructural and electrochemical characterization. Quantitative image analysis was performed using ten measurements per experimental condition for the determination of the fine pearlite fraction, MnS inclusion density, and pearlite interlamellar spacing. Corrosion resistance was evaluated by potentiodynamic polarization in a 3.5 wt.% NaCl solution using a scan rate of 0.1667 mV/s over a potential range of ±0.5 V with respect to the corrosion potential. Five measurements were performed for each specimen, and the reported values represent mean values. Statistical differences among the evaluated conditions were assessed by one-way ANOVA (p < 0.05). The gray cast iron preconditioned with metallurgical coke exhibited the highest MnS inclusion density (226 ± 5 MnS/mm²), the largest fraction of fine pearlite (55.35 ± 0.84%), and the smallest pearlite interlamellar spacing (170 ± 3.50 nm). Correspondingly, this alloy exhibited the lowest corrosion current density and corrosion rate (0.016 ± 0.002 mm/year), representing an approximately 65% reduction compared with the alloy preconditioned using electrode graphite. The results indicate that the improved corrosion resistance is associated with the combined influence of the selected preconditioning material and the resulting metallurgical conditions, including differences in sulfur content, Mn/S ratio, carbon equivalent, MnS inclusion density, and pearlite refinement. These findings demonstrate that appropriate selection of the preconditioning material can modify the solidification behavior and microstructural evolution of gray cast iron, thereby improving its corrosion performance in aggressive environments. Keywords: Corrosion resistance, Pearlitic microstructure, Gray iron, Preconditioning materials.