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

• Pre-cryogenic treatment before tempering can cause a 5-fold increase in the RCF life of M50 steel compared with post-cryogenic treatment. • More secondary nanocarbides with a diameter of 20–50 nm are formed via pre-cryogenic treatment before tempering. • Post-cryogenic treatment results in the decomposition of the retained austenite into ferrite and carbides, while Pre-cryogenic treatment promotes the transformation of the retained austenite into fresh martensite with a finer twin structure. • The huge improvement of RCF life by pre-cryogenic treatment is jointly caused by the uniformly distributed secondary nanocarbides and the formation of more and finer twinning, which suppress the initiation and growth of cracks during fatigue loading. 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 L 10 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. [Display omitted] [ABSTRACT FROM AUTHOR]