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

Abstract

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.