Effect of austempering temperature on microstructure and tribological behaviour of hypoeutectic austempered ductile iron alloyed with copper

Abstract

In the present work, Cu alloyed ductile iron was isothermally treated at five different temperatures (280°C, 300°C, 320°C, 350°C, and 380°C) for 1 h to obtain an ausferrite microstructure composing a very fine ferrite phase and carbon enriched austenite. Microstructural characteristics exhibited a high ultimate tensile strength of 950–1600 MPa of ADI comparable to or even stronger than forged steels. The bulk hardness was 460–288 HV10, higher than pearlite, but lower than pure martensitic. The tribological behaviour of ADI was investigated using a 10 mm pin diameter during sliding. Its friction coefficient decreased almost by half as compared with ductile iron due to its ausferritic morphology and carbon enrichment. Under oxidative and adhesive conditions, an austempered microstructure with very fine ferrite and high carbon austenite is most wear-resistant due to its adequate strength, toughness, and lubricative behaviour. Wear resistance of ADIs can be improved through tailoring microstructure through austempering.