Cyclic deformation and fatigue behaviour of microalloyed carbon steels for use in railway wheels

The low-cycle fatigue behaviour of two V-N microalloyed carbon steels has been studied. The materials were manufactured in the form of railway wheels, which puts severe constraints on deformation and on cooling rates. The reference is a standard wheel steel, while a modified version is created by increasing the N content, by homogenisation and by forging at lower temperatures, leading to a more fine-grained microstructure. In both materials cyclic softening occurs during a considerable portion of the lifetime at lower strain amplitudes, while at larger strain amplitudes, a constant stress amplitude is found for the whole lifetime. The stress amplitudes are lower for the modified material at given strain amplitudes, while the Coffin-Manson plots indicate superiority for this material in strain-controlled fatigue.