Effect of Different Heat Treatment Parameters and Copper Addition on the Mechanical Properties of Austempered Ductile Iron (ADI)

Abstract

Ductile Iron or Spheroidal graphite cast iron (SGCI) has graphite in the form of spherical nodules, instead of flakes as found in grey cast iron. The spherical shape of the graphite is obtained by inoculation of grey cast iron melt with Magnesium or Cerium. These graphite nodules are the core reason for the improved ductility of the ductile iron in as-cast form.But ductile has very low industrial utility in as-cast form. Therefore, to enhance the mechanical properties of ductile iron,copper addition and austempering has been performed. Austempering was performed for both unalloyed and copper alloyed ductile iron samples at different
austempering temperatures of 275,325 and 375 degrees Celsius respectively for 30, 60, 90, 120, 150, 180 minutes of austempering times respectively. For microstructural characterization Scanning Electron Microscopy and X-Ray Diffraction Analysis has been performed.The observed microstructure of ADI is essentially Ausferrite, a mixture of ferrite and carbon enriched or stabilized austenite, which changes with the change of austempering parameters. For investigating the different mechanical properties like Tensile Strength, yield strength, percentage of elongation and hardness standard tests has been carried out by following ASTM standards. For both unalloyed and copper alloyed samples, ADI austempered at 325 degrees Celsius for 120 minutes yielded best combination of mechanical properties. Copper alloyed samples were found to have more strength and hardness than, unalloyed ones.
Thus,the developed copper alloyed austempered ductile iron can be successfully used for automobile or after market industry where high tensile strength, toughness and optimum hardness is required along with high strength to weight ratio. A detailed representation in that context has been presented in the present work.