Comparative Analysis of Corrosion Behavior in Compositionally Modified Hot-Rolled AISI 430F: Assessing Surface Versus Intrinsic Substrate Characteristics

The experimental work described in this study was aimed at investigating the corrosion behavior and surface characteristics of a chemically modified AISI 430 F ferritic stainless steel. The modified composition was designed to improve machinability while optimizing the magnetic properties for specific application requirements. The samples were obtained from hot-rolled coils in the as-rolled condition, prior to any subsequent heat treatment or pickling process. The material’s electrochemical response was assessed using potentiodynamic polarization curves and micrographic analysis across two distinct conditions: as-rolled and heat-treated. The characterization protocol involved a comparative evaluation of the oxide-free cross-sections (intrinsic bulk resistance) and the peripheral surface (material's response following high-temperature exposure) and for all tested conditions. This approach served a dual purpose: first, to quantify the differential electrochemical behavior between the bulk matrix and the surface oxide scale; and second, to compare the as-rolled and heat-treated states to determine the influence of thermal processing on both surface evolution and the corrosion behavior of the internal microstructure. The electrochemical results confirmed the non-protective nature of the external oxide scale and consistently indicate that the material fails to establish stable passivity across all investigated experimental conditions. Furthermore, the heat treatment modifies the microstructure and has influence on the localized corrosion morphology. This effect is mainly attributed to alterations in the electrochemical response of the MnS-based inclusions, which are deliberately engineered within this steel grade. The thermal cycle appears to modulate the galvanic coupling between the surrounding matrix and the inclusions, thereby influencing their electrochemical behavior.