Microstructures and mechanical properties of a modified high-C-Cr bearing steel with nano-scaled bainite

The microstructures and mechanical properties of a novel bainitic bearing steel subjected to austenitizing at 950 °C for 40 min followed by low-temperature austempering at 200 °C for 2 h, 6 h, 12 h and 72 h were studied. Nano-bainite microstructure with bainitic ferrite plate thickness about 50±15 nm was obtained by austempering at 200 °C for 6 h, 12 h and 72 h. Besides nano-scaled bainitic ferrite plates, there were small amount of retained austenite and undissolved carbides in the microstructure. The volume fraction of retained austenite is 7.2% in the samples austempered at 200 °C for 72 h. The ultimate tensile strength of samples austempered at 200 °C for 72 h reaches 2373 MPa, which is superior to the sample austempered at 200 °C for 2 h, whose microstructure is almost full martensite. The weight loss values are 0.0100 g and 0.0273 g for samples austempered for 72 h and 2 h respectively and the wear resistance of the sample austempered for 72 h is about 1.7 times higher than that for 2 h. Because of the excellent strength and wear resistance of the low-temperature bainite, this low-temperature austempering could be a potential technology for manufacturing bearings.