Effect of Different Heat Treatment Parameters on Mechanical Properties of DMS Ductile Iron

Abstract

In newly developed ductile iron with dual matrix structure, ferrite (soft phase) and martensite (hard phase) control the mechanical properties. The dual matrix structure is created by incomplete austenitization of ductile iron within the intercritical intervals followed by rapid cooling. The present dissertation was focused on studying the influence of intercritical austenitizing temperature, quenching media and tempering temperatures on mechanical properties of dual matrix structured ductile iron. Ductile iron (3.57 wt% C, 2.10 wt% Si) was intercritically austenitized in two phase region (α +γ) at temperatures of 790°C and 820°C for 5 minutes and then quenched in two different media, water and paraffin liquid light oil. Then tempering was done at three tempering temperature i.e. 4000C, 4500C and 5000C for 1 hr. After it XRD, optical microscope, Vickers hardness tester, FESEM were used to characterize the mechanical properties. The result shows volume fractions of ferrite and martensite can be controlled by intercritical austenitizing temperature. Mechanical properties like strength and ductility depend on volume fractions of matrix component i.e. martensite and ferrite. The ultimate tensile strength and yield strength initially drop and then remain almost constant by increasing the tempering temperature from 400°C to 500°C. FESEM shows with increase in temperature hardness increases for untempered samples but for tempering ductility increases with temperature.