Understanding the microstructural evolution and fretting wear behaviors of M50 bearing steel heat treated at different temperatures

For M50 bearing steel, which is widely used in aerospace engine main bearings, fretting wear is an important but neglected category of wear failure during engine cold startup. High temperature tempering is crucial in heat treatment to enhance its microstructure and wear resistance. In order to investigate the influence of different tempering conditions on fretting wear performance of M50 steel, it is essential to conduct a comprehensive study. This research explores how heat treatment processes affect the fretting wear properties of M50 steel by varying the tempering temperature (450 °C, 500 °C, 550 °C, 600 °C, and 650 °C). We analyzed the microstructure evolution and fretting wear behavior under different conditions using SEM, EDS, XRD and other characterization methods. The results show that the tempering temperature influences fretting wear through martensite, retained austenite, and carbide transformations. In the 450 °C–600 °C range, wear volume and wear rate decrease with hardness. At 550 °C tempering, M50 achieves the highest hardness (59.71 HRC) and a lower wear rate (9.661 × 10−8 mm3/(N·mm)). M50 steel exhibits optimal fretting wear performance at 550 °C tempering. Overall, wear behavior occurs in the mixed slip regime, shifting towards partial slip with higher tempering temperatures. When the tempering temperature is low, the fretting wear mechanism is predominantly dominated by fatigue wear and abrasive wear, while at higher tempering temperatures, the fretting wear mechanism is primarily governed by oxidative wear and adhesive wear.