Forced-Air Cooling Quenching: A Novel Technique for Austempered Ductile Iron Production

This study produced austempered ductile iron (ADI) with ausferrite structure using forced-air cooling as the quenching method. ASTM A536 65-45-12 grade of ductile iron was produced, machined into flat samples of 5, 10, 15, 20 and 25 mm thickness, austenitised at a temperature of 820 °C for 1-h soaking period inside a muffle furnace, forced-air-cooled in an air quenching chamber to an austempering temperature ( T A ) of 300 °C and rapidly transferred into another muffle furnace maintained at 300 °C in order to austemper them for a fixed period of 2 h. Finally, the microstructural morphology and phase distribution of heat-treated samples were characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD) method. The SEM image with electron-dispersive X-ray analyses shows predominant carbon and iron peaks of high-carbon austenite and ferrite, respectively, while the XRD patterns predominantly consist of austenite ( γ ) and ferrite ( α ) phases which are the characteristic features of ADI. The study concluded that with the use of forced-air cooling as a quenching method, ADI of section thicknesses up to 25 mm with ausferrite structure is producible.