Production of Austempered Gray Iron (AGI) Using Forced Air Cooling

This paper presents the outcome of the production of austempered gray iron (AGI) using forced air cooling as the quenching medium. Samples from Class 20 gray cast iron were prepared for micrographic analysis, x-ray diffraction (XRD) analysis, and mechanical testing. The prepared samples were austenitized at 920°C, soaked for 1 h, force air-cooled to the austempering temperature range of 250°C to 400°C (at 25°C intervals), held for another hour at the austempered temperature to allow for complete phase transformation, and then air-cooled to room temperature. The optical micrograph revealed a unique microstructure consisting of ferrite (α) and high carbon austenite (γHC) called ausferrite, the coarseness of which increases as the austempering temperatures increases. XRD analysis revealed only the peak of the α phase. The estimated effective particle size d_α of this phase increases with an increase in austempering temperature. The results of mechanical tests showed significant increases in the tensile strength, hardness, toughness, and ductility of austempered samples of Class-20 grade gray cast iron. Conclusively, AGI has a unique combination of high strength and ductility that makes it suitable for the manufacture of parts in which high strength, high wear resistance, and high ductility are required.