Enhancing Corrosion Resistance of Carbidic and Austempered Carbidic Ductile Iron in Chloride Solutions via Sodium Tungstate Addition

This study investigates the corrosion behavior and surface morphology of carbidic ductile iron (CDI) and carbidic austempered ductile iron (CADI) in 3.5% NaCl, focusing on the effects of heat treatments at 275°C and 375°C and alloying with Nb (0 and 1 wt.%) and Cr (1 and 1.5 wt.%). The corrosion characteristics were evaluated with and without the addition of Na₂WO₄ as an inhibitor (0.1 g and 0.2 g). At 275°C, the 1Cr-Nb alloy exhibited the lowest corrosion rate (CR) of 0.003 mm/y in 3.5% NaCl without inhibition, which further decreased to 0.001 mm/y with the addition of 0.2 g Na₂WO₄. The surface morphology of the corroded alloys reflected their corrosion behavior, revealing evidence of uniform corrosion, localized pitting, and galvanic corrosion. These findings highlight the influence of heat treatment, alloying elements, and inhibition on the corrosion resistance of CDI and CADI in saline environments.