The Austempering Kinetics, Microstructural Development and Processing Window in the Austempered, FE-۳.۲C-۴.۸AL Compacted Graphite Cast Iron

In the present study, austempering heat treatment was performed on compacted graphite aluminum cast iron with the chemical composition of ۴.۸%wt Al, ۳.۲%wt C, ۰.۸۱%wt Ni, ۰.۳۷%wt Mn, and ۰.۰۲%wt Mg. This study aims to investigate the effect of aluminum additions and removal of silicon on the kinetics of austempering transformation of Fe-۳.۲%C alloy. The cast samples were austenitized at ۹۰۰ °C for ۱۲۰ min and the isothermal austempering heat treatment was performed at ۲۰۰ °C, ۳۰۰ °C and ۴۰۰ °C for ۵, ۳۰, ۶۰, ۱۲۰ and ۱۸۰ minutes, respectively. Kinetics of this transformation was studied by X-Ray diffraction (XRD) analysis. The effect of temperature and time on the microstructure and hardness of the austempered samples was investigated and discussed. The presence of Al was seen to prolonged formation of the carbides from high carbon austenite, and that expanded the process window in the austempering transformation. Besides, the lower bainitic ferrite phase was observed in the austempered samples at ۲۰۰ °C and ۳۰۰ °C. Increasing austempering temperature to ۴۰۰ °C changed the lower bainite to upper bainite structure. The volume fraction of austenite reached its maximum level (۳۴.۶ %) after austempering the samples at ۴۰۰ °C for ۳۰ minutes.

کلیدواژه ها:

austempering kinetic ، compacted graphite ، aluminium cast iron ، ferritic bainite ، window process