The role of welding parameters on the control of the microstructure and mechanical properties of rails welded using FBW

Abstract

Heavy haul railways are increasingly being subjected to operating conditions that demand better performance of the materials, with speeds of operation and loads increasing to comply with the large demand for transportation. For joining of rails, the Flash Butt Welding (FBW) process stands out due to the higher quality of the joint with respect to thermite welding. However, the properties of the rails may be compromised because of improper parameterization of the welding process and the appearance of defects in the welded joint, as well as heterogeneities in the Heat Affected Zone (HAZ). In this work, a statistically planned experimental array was used to study four parameters of the FBW process (pulse current, number of pulses, upsetting force, and equivalent carbon) on Premium and Super Premium rail steels. The array generated eight different welding conditions. The results made it possible to understand the relationship between the microstructure and the microhardness maps on the longitudinal section of the welded joint. Fracture analysis showed the fracture mechanisms for each welding condition. The Premium rails showed double-necking in the partial austenitization region while Super Premium rails showed brittle fracture, except for the more extreme welding condition. Additionally, two welding conditions showed double-necking in the partial austenitization region, but with brittle fracture outside the necking region. Tensile tests showed that the welding condition that corresponds the highest heat input presented the worst mechanical behavior for applications on railroads and the welding conditions with lowest heat input presented the best behavior.