A Study on the effect of austempering temperature, time and copper addition on the mechanical properties of austempered ductile iron

Abstract

The most rapidly growing area of cast technology is that of ADI or Austempered Ductile Iron. ADI is a heat treated Ductile Iron or S.G. iron with a unique micro-structure: Ausferrite which consists of high carbon Austenite and Bainitic ferrite with graphite nodules dispersed in it.
This unique microstructure yields excellent properties: high strength, toughness, good wear resistance, good machinability and all that at low cost. The use of this type of cast iron as an engineering material has been increasing day by day since its discovery. These properties can be
achieved upon adequate heat treatment which yields optimum microstructure for a given chemical composition. But this type of treatment is bit tricky, since it requires controlled heating and isothermal holding of the material.
In this work an investigation has been conducted on ductile iron with and without Copper additions and austempered in a range of time and temperature. An attempt has been made to
study the effect of austempering time and temperature and the influence of copper addition on the mechanical properties of ADI. The tensile strength was found to increase with decreasing
austempering temperature with maximum tensile strength seen in samples austempered at lower temperatures, 250°C and shorter times. Maximum ductility was obtained after austempering for 1.5 hours. An increase in the ductility of ADI was found on copper addition. Hardness of both
the samples was found to be decreasing with increasing austempering time and temperature, and toughness of ADI was seen to be increasing with increasing time and temperature and was more prominent in case of ADI samples with copper.