Effect of Micro Constituents on Wear Properties of Alloyed Ductile Iron

Abstract

The current study was focused to study the behavior of DI under dry sliding wear condition and observe the effect of micro constituents, achieved by alloy addition and heat treatment processes. To carry out the study two ductile irons with different compositions were chosen, so that effect of chemical composition can be studied. The DI specimens of both alloys were then subjected to annealing, normalizing, quenching & tempering and austempering heat treatment processes to achieve different microstructure and micro constituents for the alloys. The as-cast and heat-treated specimens were then subjected to Ball-on-plate wear tester under 20N load for 5, 10, 15 and 20 minutes run. The surface morphology and wear mechanism was studied by observing under FESEM. Both the alloys achieved fully ferritic, pearlitic/ferritic, tempered martensitic and coarse upper bainitic matrix with graphite nodules lodged into the respective matrices after subjected to annealing, normalizing, quench & tempering and austempering heat treatments respectively. Whereas the as-cast microstructure for alloy SG-1 was found to be ferritic and that of alloy SG-2 was Bull’s eye ferritic/pearlitic. The Bull’s eye ferritic/pearlitic matrix resulted in higher hardness of SG-2 as-cast specimen than that of SG-1 as-cast specimen with ferritic matrix. Quench and tempering treatment resulted in transformation of as-cast matrix into hard brittle tempered martensitic matrix whereas austempering treatment was resulted in bainitic matrix transformation. The specimens when subjected to Ball-on-plate wear system it was observed that soft annealed and austempered specimens had maximum wear compared to as-cast, normalized and quench & tempered specimens. This behaviour was attributed to the hardness of respective material. Alloy SG-1 was observed to lower wear rate than that of SG-2 due to its higher hardness. The wear behaviour when studied for individual alloys it was observed that specimens subjected to higher cooling rate had better wear resistance due to their hardness but simultaneously considerable wear was also observed due to the increased nodule count that encourages more sites for material removal. The wear was observed to increase linearly with time for all of the heat treated specimens. An adhesive wear phenomenon was observed for as-cast and annealed specimens characterized by the presence of delaminated layer over the worn surface. Whereas for normalized, quench & tempered and austempered specimens plastic deformation was observed characterized by the cracks over the worn surface.