Impact of heat treatment on mechanical and tribological behaviour of unalloyed and alloyed ductile iron

Abstract

The impact of heat treatment process (HT) on microstructural, mechanical and tribological performance of unalloyed and alloyed ductile iron has been investigated. Austenitizing temperature at 900 °C/350 °C/30min, 920 °C/350 °C/30min, 950 °C/350 °C/30min and 970 °C/350 °C/30min were deployed respectively, after which the specimens were furnace cooled to room temperature. The highest ultimate tensile strengths of 598.9 and 519.75 Mpa were recorded for both unalloyed and alloyed ductile iron (DI) at 920 °C/350 °C/30min. The DI heat-treated at 950 °C/350 °C/30 min from the Charpy impact test had the highest energy value of 10 J. The optical microscope and SEM micrographs show that heat-treatment process produced some ferrite and martensitic structures; some bull eyes and nodules are also evident on the microstructures. The highest frictional coefficient value of 9.10 × 10 −1 was obtained for DI matrix while 8.0 × 10 −1 , 6.0 × 10 −I , 4.0 × 10 −1 and 2.0 × 10 −1 were recorded for specimens heat-treated at 900 °C/350 °C/30min, 920 °C/350 °C/30min, 950 °C/350 °C/30min and 970 °C/350 °C/30 min, respectively. In addition, the tribological behavior of the heat-treated DI under 10 N loads showed a dual wear process comprising abrasion and oxidation. The wear behavior of the heat-treated microstructure in the matrix corresponds to the strengthening and toughening effect under the same load. However, the mechanical testing of the samples confirmed an improvement in the hardness, impact, and tensile strength of the samples. The significance of annealing heat treatment is demonstrated in this study, as its consistent impact is evident in all the mechanical tests conducted on the specimens.