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A novel nanobainitic (NB) steel is treated by three different heat treatment routes: quenching-tempering (QT), quenching-austempering-tempering (AT), and quenching-austempering-deep cryogenic treatment-tempering (ACT). To investigate the effects of retained austenite (RA) with different morphologies, stabilities, and volume fractions on the wear resistance of NB steel, the microstructure is observed by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The volume fraction and stability of RA are determined by quantitative X-ray diffraction (XRD) analysis. It is found that deep cryogenic treatment (DCT) after low-temperature austempering can effectively eliminate the blocky RA, increase the stability of filmy RA and have no effect on the NB microstructure. The AT and ACT treatments have higher surface residual compressive stress and better wear resistance than conventional QT treatments. For the ACT treatment, a multiphase microstructure composed of NB, martensite, and filmy RA is obtained near the surface, and the wear resistance of the steel is optimized, with increases of 23%, 52%, and 93% for austempering times of 8, 12, and 24 h, respectively. The results show that DCT can be combined with low-temperature austempering treatment, thereby effectively eliminating unstable blocky RA, avoiding the transformation of brittle martensite, and obtaining improved wear resistance.

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A novel methodology of carbon‐diffusion‐dominated continuous cooling treatment (CC) during the bainite transformation is proposed and implemented on a high‐carbon nanobainitic steel. Nanobainite (NB) microstructure composed of bainitic ferrite lath with a thickness of ≈36 nm is obtained by successive heat treatment processes, including cooling the sample from 240 to 216 °C at a rate of 0.1 °C min−1, then cooling down to 120 °C at a rate of 0.2 °C min−1 followed by austempering at 120 °C for 12 h. Several technological routines involving oil quenching + tempering, single‐stage austempering + tempering, and two‐stage austempering + tempering are compared. The effects of heat treatment processes on the microstructure and mechanical properties are unveiled. Importantly, after the CC process, the tensile strength is 2049 MPa, the yield strength is 1552 MPa, the elongation is 2.5%, the impact toughness is 11.5 J, and the hardness is 60.7 HRC. Notably, the comprehensive mechanical properties of CC‐processed samples are superior to that of other heat‐treated samples. Microstructure analyses reveal that the CC process significantly refines the bainitic ferrite lath thickness while increasing the volume fraction of NB. Thereby, effectively shrink blocky retained austenite, and finally enhancing the overall mechanical properties.