This study investigates the microstructure, mechanical response, and corrosion resistance of AISI 9840 machinery-grade steel subjected to powder-pack boriding at 950 °C for 2, 4, and 6 h using Durborid G powder. X-ray diffraction (XRD) confirmed the exclusive formation of the Fe2B phase. The borided layer exhibited a dense saw-tooth morphology with thicknesses ranging from 67 ¿m to 109 ¿m, as revealed by scanning electron microscopy (SEM). Nanoindentation analysis showed that the indentation hardness (HIT) exceeded 20 GPa. Gravimetric corrosion tests performed in 1 N H2SO4, together with electrochemical polarization measurements, revealed a significant reduction in corrosion rate after boriding, with further improvements observed as treatment time increased. The corrosion current density decreased by more than one order of magnitude in borided samples, confirming the protective effect of the Fe2B layer. A Design of Experiments (DoE) was applied to the borided conditions to evaluate the influence of treatment time and acid exposure time on mass loss. The results indicated that exposure time was the dominant factor, while increasing boriding time contributed to reducing corrosion. The electrochemical response confirmed the superior protective behavior of thicker boride layers, characterized by lower corrosion current densities and enhanced stability in acidic media. These results demonstrate that powder-pack boriding significantly enhances the surface hardness and corrosion resistance of AISI 9840 steel, while longer treatment times further improve its performance.
