<p>This study investigates the effect of isothermal aging at 1000&#xa0;°C on the microstructural evolution and corrosion behaviour of UNS S32750 super duplex stainless steel (SDSS) aged for 15, 30, 45, 120, and 420&#xa0;min. Aging promoted the eutectoid decomposition of ferrite (α) into sigma (σ) and secondary austenite (γ₂) phases, resulting in a substantial reduction in α phase fraction from 61.19% in the as-received condition to 1.77% after 420&#xa0;min, accompanied by an increase in total secondary precipitates (γ₂ + σ + χ) from 0 to 59.64%. The σ-phase fraction increased progressively to 13.01%, while the γ₂ phase reached 44.21% after prolonged aging. Potentiodynamic polarization and ASTM G48 immersion corrosion tests revealed a significant deterioration in corrosion resistance with increasing aging time. The corrosion current density increased from 0.26&#xa0;mA&#xa0;cm⁻² for the as-received sample to 3.01&#xa0;mA&#xa0;cm⁻² after 420&#xa0;min of aging, while the pitting potential decreased from 766 to 413 mV_SCE. The degradation in corrosion performance is attributed to the precipitation of Cr- and Mo-rich σ phase, which generates Cr- and Mo-depleted regions in the surrounding matrix, promoting localized corrosion. Microscopic examination of corroded surfaces confirmed preferential pit initiation at phase boundaries and transformed regions associated with secondary phase precipitation. Optical profilometry further revealed a marked increase in average surface roughness (R_a), with R_a increasing from 25.4&#xa0;nm in the as-received condition to 385.7&#xa0;nm after 420&#xa0;min of aging, indicating severe localized attack. The results demonstrate that secondary phase precipitation during isothermal aging significantly degrades the corrosion resistance of SDSS by promoting micro-galvanic corrosion and localized dissolution through the formation of Cr- and Mo-depleted regions.</p> Graphical Abstract <p></p>