Exploring the ultrahigh rolling contact fatigue life of M50 bearing steel by adjusting the cryogenic sequence

The influence of different cryogenic sequences on the rolling contact fatigue (RCF) life of M50-bearing steel has been studied. The results show that direct cryogenic treatment after quenching can effectively improve RCF life. The L10 life is strikingly 5 times longer than that with cryogenic treatment after tempering. This is caused by the distinct lattice construction of martensite and the transformation of retained austenite. More secondary nanocarbides and fine twins are formed via cryogenic treatment before tempering compared with cryogenic treatment after tempering. The improvement in the RCF life of the steel is attributed to the joint effects of the secondary nanocarbides and twin boundaries with a width of 5–13 nm, which delays significantly crack initiation and propagation. This study highlights a common method to improve the service life of high-carbon and high-alloy steels by adjusting the cryogenic sequence.