Effects of Multiple Repair Welds at Rail Head to Serviceability

Railway tracks on severe routes such as curved tracks and slope tracks are usually found damage at rail heads, and they need to be repaired repeatedly. During servicing period, the damaged rail heads are welded multiple times at the same locations. The effect of multiple times welding on mechanical properties and microstructures of rail heads has not been studied. This study aims to reveal the effect of multiple weld cycles from 1st to 4th time on R350HT rail heads. The welding process was SMAW with UTP-DUR-350 hard-facing electrode. Vickers hardness surveying and SEM metallography were used to determine the results related to the number of repairs. The results showed that the weld HAZ was distinguished as black zone and soft zone. In the black zone, hardness was 385 - 395 HV₁₀ which is the hardest zone while in the soft zone, hardness was 275 - 310 HV₁₀. The hardness in the soft zone was decreased corresponding to the number of repairs. The SE-SEM micrographs at the soft zones revealed that lamella cementite structures were transformed into spheroidal particles. The microstructures in the black zone generally consisted of lamella pearlite and grain boundary ferrite. Moreover, in the 4th repair, Widmanstätten structures were observed at grain boundaries of the black zone HAZ.