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Improvement of Abrasion Wear Resistance of Ductile Iron by Two-Step Austempering

Abrasion wear rates of conventional and two-step austempered ductile cast iron (ADI) were investigated. Conventional austempering and two-step austempering processes were carried out at 280, 300, and 320°C. Microstructures revealed that higher austemperig temperature resulted in coarser ausferrite and higher volume fractions of blocky retained austenite. The ausferrite in two-step austempered ADI was slightly coarser comparing to the coventional ADI since the temperature was raised by 30°C during austempering. Two-body abrasion wear rates of ADIs were studied using a Suga abrasion wear tester. It was found wear rates of the two-step ADI become significantly lower than those of the conventional ADI, especially when the austempering was carried out at low temperature, i.e. 280°C. Such behavior was due to the strong influence of high carbon concentration in retained austenite eventhough the ausferrite matrix was coarser.