Effect of microstructure on abrasion wear behavior of austempered ductile cast iron (ADI) processed by a novel two-step austempering process

An investigation was carried out to examine the influence of a novel two-step austempering process on microstructural parameters and the abrasion wear resistance of austempered ductile cast iron (ADI). Two batches of cylindrical pin specimens were prepared from an alloyed nodular ductile cast iron and were initially austenitized at 927 °C (1700 °F) for 2 h. The first batch of samples was austempered by the conventional single-step austempering process at five different temperatures, e.g., 288 °C (550 °F), 316 °C (600 °F), 343 °C (650 °F), 371 °C (700 °F), and 385 °C (725 °F) for 2 h, whereas the second batch of samples were processed by the two-step austempering process. These samples were initially quenched in a salt bath maintained at 260 °C (500 °F) and then the temperature of the salt bath was raised to interfacial austempering temperatures316 °C, 343 °C, 371 °C and 385 °C. These samples were austempered at these temperatures for 2 h. The test results show that this two-step austempering process has resulted in significant improvement in microstructural parameters (such as higher volume fraction of austenite, Xγ, higher carbon content in austenite, Cγ, finer ferritic cell size, d, as well as higher total carbon in the matrix, XγCγ). Two-step process has also resulted in significant improvement in abrasion wear resistance in ADI, compared to the conventional single-step austempering process.