Effect of Two-Step Austempering Process on the Microstructure and Mechanical Properties of Low-Carbon Equivalent Austempered Ductile Iron

Low-carbon equivalent austempered ductile iron (LCE-ADI) exhibits high modulus of elasticity than conventional austempered ductile iron (ADI) due to less graphite content. Austempering parameters of temperature and time significantly influence the mechanical properties of LCE-ADI. In the present work, response of the material to two-step austempering in the range of 350–450°C was studied, and a comparison was made to single-step austempering. Reduction in ferrite cell size, increase in % carbon in carbon-stabilized austenite (CSA) and increase in volume fraction of CSA led to increase in tensile strength (10%) and hardness (20%), in addition to improved toughness (10%).