Effects of Carbon Content in Parent Austenite on Tribological Behavior of Austempered Ductile Iron

The carbon content in parent austenite significantly affects the phase transformation during the subsequent heat treatments. By tailoring the carbon content in parent austenite, the resultant microstructure and wear properties of ADI were investigated in the present study. The austempered samples are composed of acicular ferrite (alpha) and reacted metastable austenite (gamma). Low carbon content in parent austenite increases the amount of alpha but reduces its size, while high carbon content increases the carbon concentration and volume fraction in gamma. Consequently, low carbon content in parent austenite gives rise to a high strength but a decreased plasticity. Wear tests indicate that the run-in period of the sample with high carbon content in parent austenite is half compared with low carbon content, which is a consequence of a more rapid surface smoothing and stabilization caused by low hardness. As the load increases, the friction coefficient (mu) of both samples ranges from 0.35 to 0.48, and wear volume loss ranges from 0.029 to 0.040 mm3. Low carbon ADI, with higher hardness, primarily experiences adhesive wear under low loads, transitioning to a mix of adhesive and abrasive wear at high loads. In contrast, high carbon ADI, with lower hardness, consistently exhibits a combination of abrasive and adhesive wear regardless of the load.