Influence of HAZ microstructure on RCF under twin-disc test of a flash-butt welded rail

A new twin-disc test was performed using discs containing all microstructures of the heat-affected zone (HAZ) of flash-butt welded rails. It was observed that the lower hardness regions (spheroidized cementite in a ferritic matrix) at the HAZ boundary underwent a local deformation, generating valleys and reproducing a common defect type observed in rail welds: double squat-like defect. Longer crack lengths or crack clusters were observed in the HAZ boundary and central weld regions. The cross-section metallography showed that these cracks are directly related to the microstructure of spheroidized cementite at the HAZ edges or pro-eutectoid ferrite at the central region. The decrease in surface roughness before the cracks, the presence of oxide on the bottom crack surface, and superior spheroidized cementite microstructure in the upper crack region suggest that these larger/cluster cracks are predominated by extrusion of the softer material above the harder material (pearlitic/base metal).