Laser cladding: The alternative for field thermite welds life extension

Abstract

Thermite field welds are the link of rails; however, they experience plastic deformation (batter) along the area above the heat affected zone (HAZ). Here we present the benefits of using laser cladding to minimize the plastic deformation on the HAZ. Our test consisted of a laboratory and a full scale approach under the most extreme revenue service conditions known in North America. The laser cladding coatings were used in the past for rails but its life was terminated in their infancy (after approximately 3–4MGT) due to the presence of un-tempered martensite that negatively affected the rail toughness. The new tested laser cladding design is capable of producing a sound coating with tunable hardness (from 360–430HBN). This is possible through a new heat treatment procedure carried using a propane torch or induction heating at temperatures between 400 and 500°C and cooling rates below 3°C/s. The microstructure shows that the rail after laser cladding is fully pearlitic. The laser cladded welds sustained up to 42milliongrosstons in heavy haul traffic that is between 1000 and 1400% improvement when compared to other previous works.