Influence of nodular graphite on microstructure, mechanical properties, and wear behavior of austempered ductile iron

This study systematically investigated the effects of graphite nodule parameters, including count, average diameter, and nodularity, on microstructure and mechanical properties of austempered ductile irons (ADIs). The ADI specimens with graphite nodule counts of 212±11 mm-2, 308±9 mm-2, 415±10 mm-2, and 589±13 mm-2 were designated as G-200, G-300, G-400, and G-600, respectively. Results indicate a progressive refinement of graphite with an increase in nodule counts. Specifically, the average nodule diameter decreases from 33.3±1.3 μm for G-200 to 17.0±0.7 μm for G-600. The nodularity of all samples are above 90%. Furthermore, the nodularity exhibits a corresponding increasing trend with the rise of graphite nodule count in ADIs. Additionally, the volume fraction of the austenite phase in ADIs decreases with an increase in graphite nodule count. The graphite nodule count changes the tensile strength and elongation of ADIs. The specimen G-400 exhibits the ultimate tensile strength of 897±11 MPa and an elongation of 9.8%±0.6%, representing 5.3% and 44.1% improvements respectively compared to G-200. To explore the wear resistance of ADIs with different graphite nodule counts, dry sliding friction and wear test of different samples was carried out at room temperature. At a high load of 25 N, G-400 exhibits superior wear resistance, achieving a 42% reduction in worn volume compared to G-200. Worn micromorphology identifies three primary wear mechanisms: microcutting-dominated abrasive wear, adhesive wear, and fatigue wear.