Microstructural evolution and dry sliding wear behavior of composite shear flow casting M50 steel under different tempering conditions

The mechanical properties of M50 steel, which is widely used in aerospace engine bearings, are significantly influenced by its heat treatment process. This study systematically investigates the effects of tempering at different temperatures (450 °C, 480 °C, 510 °C, 540 °C, 570 °C, and 600 °C) on the microstructural evolution and dry sliding wear behavior of Composite Shear Flow Casting (CSFC) M50 steel. The microstructures under various heat treatment conditions were characterized using scanning electron microscopy (SEM), Transmission electron microscope (TEM), and energy-dispersive spectroscopy (EDS). The results show that, with increasing tempering temperature, both the average friction coefficient and wear volume of CSFC-M50 steel initially decrease and then increase. The optimal tribological performance is achieved at 510 °C, with an average friction coefficient of 0.555 and a wear volume of 3.17 × 10 7 μm 3 . This trend is attributed to the differing temperature sensitivities of carbide precipitation, which slows down, and carbide coarsening, which accelerates. During the wear process, a dense Cr-rich oxides film forms on the surface via oxidation, acting as a self-lubricating layer that reduces wear and enhances surface resistance. The dominant wear mechanisms include oxidative wear, abrasive wear, and adhesive wear.