Fatigue Crack Growth Behavior of Eutectoid Steel Rail

The fatigue crack behavior of U75V rail under different quenching rates was studied using SEM and CLSM. The results show that the pearlite interlayer spacing and fatigue crack growth rate decrease, and the deflection path of cracks and the number of branching cracks of U75V rail increases with an increase of cooling rate. The tearing edge of unstable region transites from pearlite lamellae to dimple. The fatigue crack growth path is closely related to the orientation of lamellae in pearlite microstructure. There are three modes direction of fatigue crack growth path and pearlite lamellar, which are parallel, vertical and 45° angle, and most of the branch cracks occur at an angle of 45 ° between the lamellar direction and the crack direction. More specifically, the deflection paths of cracks and branching crack have a relaxation effect on the stress intensity at the crack tip, which restrains the fatigue crack growth rate.