Austempering Temperature and Isothermal-Holding Effects on the Microstructure and Mechanical–Tribological Response of Si–Mo Alloyed Ferritic Ductile Iron Produced by SSF

This study investigates the impact of austempering temperature and isothermal-holding time on the microstructure, mechanical behavior, and tribological performance of Si–Mo alloyed ferritic ductile iron. The material is produced via the solution-strengthened foundry (SSF) route. Specimens were subjected to austenitization at 900 °C for 90 minutes, followed by salt bath austempering at temperatures of 300, 350, and 400 °C for holding durations of 30 and 90 minutes. The research demonstrates that these specific austempering parameters significantly influence the evolution of the ausferritic matrix, the characteristics of retained austenite, and the resulting mechanical and tribological responses. Notably, the material austempered at 300 °C for 30 minutes exhibited superior ultimate tensile strength

(1344.8 MPa) and hardness (52.92 HRC), alongside the lowest specific wear rate. Conversely, an austempering condition of 300 °C for 90 minutes yielded the highest impact energy (54.7 J). These findings suggest that lower austempering temperatures promote a finer ausferritic structure, leading to enhanced strength and wear resistance. Longer isothermal holding at the same temperature, however, appears more beneficial for improving impact toughness. Microscopic analysis, including SEM, revealed the presence of abrasive, adhesive, and oxidative wear mechanisms.

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