Abstract: The loading test of the new developed 60Mn2SiCr super-bainitic steel which is previously austenitized at 900 ℃ for 30 minutes and then isothermal treated at 260 ℃ for 12 h in a salt bath furnace is carried out on the fatigue testing machine for the research of the phase transformation of retained austenite induced by stress in super-bainite microstructure and its effect on the mechanical property of the steel. The microstructure morphology, phase composition and mechanical property of the loaded sample are analyzed comparing with the one without loading test by the scanning electron microscope(SEM), transmission electron microscop(TEM), X-ray diffracmeter(XRD) and tensile testing machine. The results show that the microstructure of the experimental steel after isothermal transformation is the typical super–bainite microstructure(BF+AR). The volume fraction of retained austenite is 9.4% and the average carbon content is determined as 1.296%. However, after the loading test, the volume fraction of retained austenite drops to 6.1% and the carbon content increases to 1.439%. Meanwhile, the product of tensile strength and ductility increases nearly 20%. This illustrates that the mechanical property of the steel is improved obviously by the loading stress owning to the transformation induced plasticity(TRIP) effect of retrained austenite in super-bainite microstructure.

Key words: retained austenite, super-bainite, transformation induced plasticity(TRIP)