To Study Effect of Austempering Time and Temperature On Spheriodal Graphite Iron

The Spheroidal Graphite Iron is known for its good elongation or ductility (from the beginning of the casting process only) at the part of low tensile strength. So an experimental research was conducted on ADI (with an alloy composition having relatively higher percentage of Cu) for improving the tensile strength, hardness and elongation with the variation of austempering temperature and different time periods. The variables, austempering temperature were 350°C and 400°C and holding time periods of 0.5hr and 3hrs. Experimental resultsproved that with an increase of austempering temperature and time, both tensile strength and hardness decrease whereas elongation increases. Light microscopy was utilized to investigate the bainitic transformation, while tensile tests were conducted for determining mechanical properties. By austempering at 350°C for.05hr and 3h, a microstructure comprising a mixture of free bainitic ferrite and carbon rich retained austenitewas observed. Also, appearance of martensitic structure is the characteristic of austempering at400°C is. This appearance of martensite afteraustempering at400°C remains the main cause for much lower tensile properties than at 350°C.