Transformation Characteristics and Microstructure of Rail under Low Stress during Continuous Cooling

To obtain a better understanding the thermal stress of a rail, the thermal simulator was used to measure the expansion curves of different stresses loaded during the continuous cooling process of U75V rail. The transformation plasticity model was established. The experimental results show that stress can accelerate the transformation process of pearlite. While the same cooling rate is accelerated with the increase of stress, the transformation process of pearlite is accelerated, and the proportion of plastic strain transformation in total strain increases. At the same stress, the process of transformation of pearlite decreases with the increase in cooling rate, and the proportion of transformation plastic strain in total strain decreases. When considering the transformation plasticity, the axial residual stress is more consistent with the actual working condition, the accuracy of the transformation plasticity model is higher; during the continuous cooling process, and the loading stress has a significant influence on the structure. When the stress increases, the orientation of the pearlite lamellae becomes disordered, the pearlite lamellae are bent, the lamellae spacing is no longer uniform, and the hardness is improved.