Abstract

The heat-affected zone (HAZ) of a thermite weld contains softer parts that are weak and need to be modified for best rail performance. This study examines how welding heat inputs of FCAW, and preheating temperatures affect the microstructure and hardness of its weld metal and HAZ after repairing the weak area of thermite welded rail. To improve the weak area’s microstructure and hardness without degrading the original thermite-welded rail, a groove was carved from the center of the HAZ on the rail head and filled using flux-cored arc welding. The investigation used two welding currents and preheating temperatures referred to as FCAW 1 and FCAW 2. The optical and electron microscopic characterization of the pearlite microstructure and interlamellar spacing were carried out. Additionally, micro-Vickers hardness testing is done. The typical hardness of the HAZ in FCAW 1 was 410 HV, whereas, in FCAW 2, it was 340 HV. The interlamellar spacings of HAZ in FCAW 1 and FCAW 2 are 80 and 105 nm, respectively. The faster cooling made pearlite interlamellar spacing finer. The decrease in lamellar spacing leads to an increase in hardness. For thermite welded rail head surface HAZ repair, greater heat input and preheating temperature with slow cooling rate work.