Investigating the Microstructure and Rolling Wear of the Laser Additive Repair Layer for Severely Damaged Rail under Extreme Loads

With the rapid development of high-speed and heavy-load railways, the occurrence of severe rail damage has become inevitable, and existing conventional repair techniques are insufficient to effectively address these damages. Laser additive repair technology offers a viable solution to this issue. However, this technology has not been validated for wheel-rail contact performance under extreme heavy-load conditions. Therefore, this paper first investigates the optimal process range by analyzing the macrostructure, microstructural morphology, and microhardness of the repaired layers produced under different processes. Subsequently, the performance of the repaired rail under extreme heavy-load conditions (300 kN vertical force and 50 kN lateral force) was evaluated using a wheel-rail contact testing rig. The results indicate that lower laser power leads to defects such as unmelted powder and pores, while higher power results in a deeper heat-affected zone (HAZ). The repair layer primarily consists of pearlite and ferrite, with martensite forming in the HAZ. Furthermore, after accumulating a throughput of 55 wt, the repair layer did not exhibit any failure. The abrasion of the repair layer was significantly higher than that of the rail base material, being 3.39 times greater. The hardness and wheel-rail forces exhibited significant changes within the throughput range of 0-18 wt. Upon reaching 21 wt, these parameters stabilized, with the hardness measured at 400 HV for the repair layer and 360 HV for the base metal. The vertical force stabilized at 181 kN, and the lateral force at 63 kN, indicating that the system had reached a steady wear stage.