Effect of inhomogeneity on crack initiation for wear-resistant U75V rail treated by laminar plasma

The surface discrete hardening of laminar plasma (HLP) is an effective method of improving wear resistance for rails. While fracture failures on as-treated rail heads are still unavoidable and the related crack mechanism is unclear. As-treated U75V rail and untreated standard U75V rail were installed simultaneously on railway for comparison. The wear form and cracking mechanism of the rails after service are studied in detail. The results show that wear resistance of HLP-treated rail is improved dramatically compared with untreated ones. The wear depth of HLP-treated rail serviced for 9 months is still less than that of standard rail serviced for only 3 months. Central ablation induces overheated structures and hot cracks, resulting in cracks within the quenched area. Decarburized layer is the main reason for a ring-shaped reticular ferrite existing at the quenched area edge. Crack initiation at the interface is facilitated by the presence of reticulated ferrite and a non-uniform microstructure formed at the surface edge of the quenched area. These cracks propagate solely within the quenched area, preventing their propagation into the interior of the HLP-treated rail.