The Effect of Cryogenic Treatment on Hardness, Toughness, and Tribological Properties of Austempered Ductile Iron with Different Nickel Contents

Abstract

Austempered Ductile Iron (ADI) is a candidate material to replace case-hardened steel in many applications. The mechanical properties of ADI can be tailored by the chemical composition and heat treatment conditions. In this study, different nickel content Ductile Irons (DI) were cast and heat treated. In order to design the austempering process, time-temperature-transformation diagrams were generated with the Calculation of Phase Diagrams method. For each chemical composition, one group was tested in its as-cast state while the second and third groups were austempered. For austempering, the casting is reheated to austenitization temperature (900 °C) and then quenched in a salt bath at a temperature of 300 °C and held at this temperature for 2 h. The third group was cryo-treated (-196 °C for 6 h) and tempered (200 °C for 2 h) after the austempering process. Microstructural examination was performed using an optical microscope and X-ray diffraction technique. The effect of heat treatment on the hardness, toughness, and tribological behaviors of samples was investigated. The results showed that austempering with correct parameters significantly improved the hardness, toughness, and wear resistance of DI. The nickel content of DI plays a significant role in determining the properties of the alloy, and the optimum Ni amount among the tested compositions was found to be 1.64%. It was observed that cryogenic treatment facilitates some of the austenite to martensite transformations and improves wear resistance (20%); however, it has a limited effect on hardness (2-3 HRc) and toughness (±3 J).

A Bidimensional Finite Element Study of Crack Propagation in Austempered Ductile Iron

“…Furthermore, ADI exhibits superior mechanical strength, ductility, toughness, fatigue resistance and wear resistance compared to other cast irons [2]. The mechanical properties of ADI are also influenced by the heattreatment temperature, which affects the microstructure of the material [6][7][8][9].…”