Corrosion Behavior Of Ductile Iron Research Articles

Effects of Copper and Austempering on Corrosion Behavior of Ductile Iron in 3.5 Pct Sodium Chloride

Although alloying and heat treatments are common industrial practices to obtain ductile irons with desired mechanical properties, related information on how the two practices affect corrosion behavior is scarce. In this study, two ductile irons—with and without 1 wt pct copper addition—were austempered to obtain austempered ductile irons (ADIs). Polarization tests and salt spray tests were conducted to explore how both copper-alloying and austempering heat treatments influenced the corrosion behavior of ductile irons. The results showed that the corrosion resistance of 1 wt pct copper-alloyed ductile iron was better than that of the unalloyed one, while ADI had improved corrosion resistance compared with the as-cast. In particular, the ductile iron combined with the copper-alloying and austempering treatments increased the corrosion inhibition efficiency up to 84 pct as tested in 3.5 wt pct NaCl solution.

Effect of austempering temperature and time on corrosion behaviour of ductile iron in chloride and acidic media

PurposeThe aim of this paper is to study the effect of heat treatment temperature and time on the corrosion behavior of ductile iron in 0.5 M NaCl and 0.5 M H2SO4.Design/methodology/approachDuctile iron samples of known composition were austenized at temperatures 800°C and 850°C, and austempered at 300°C and 350°C for periods of 30, 45 and 60 min to convert them to austempered ductile iron (ADI). The corrosion behavior of these ADI samples in 0.5 M NaCl and H2SO4 was measured using the conventional weight loss method. The metallographic examination of the samples was carried out to study the morphology of their corroded surfaces.FindingsDuctile iron is susceptible to corrosion in both acidic and chloride media, while attack by acid media is mainly at the grain boundaries, that from the chloride is pitting. The corrosion behavior of the material is affected by the compositional structures of the materials as well as the austempering temperature and time it was subjected to.Practical implicationsDuctile iron has the potential to replace costlier materials in many engineering and structural applications.Originality/valueThe results revealed that the corrosion of ADI in both acidic and chloride media were strongly dependent on the structure of the material, which in turn was affected by the austempering temperature and time.