Optimization of Mechanical Properties for Spheroidal Graphite (SG) Iron Through Various Heat Treatment Processes

Heat treatments are carried out on spheroidal graphite (SG) iron. Casting in the form of slabs is cut and machined into standard tensile test samples. These samples are heat-treated by austenitizing at 900 °C temperature, and different samples are given annealing, normalizing, quenching, tempering, and austempering treatment. A copper coating is given at the surface of the sample to prevent oxidation during austenitizing. These samples are tested for tensile testing in Shimadzu universal testing machine. Its fractures are characterized using scanning electron microscopy (SEM) and microstructure by optical microscopy. It is found that among all the categories of heat treatment, austempering heat treatment gave the best combination of strength and ductility. Hardness is found to be highest for the sample which has been quenched and tempered at 250 °C. As the tempering temperature increases, hardness, as well as yield strength, is found to be decreasing while ductility increases. The sample which has been annealed recorded the highest elongation of 24%, though at a lower yield strength of 243 MPa. The maximum ultimate tensile strength is recorded by austempered ductile iron which is also called ductile iron (DI).