Microstructure and residual stress variations in weld zone of flash-butt welded railroads

In the weld zone and base metal contiguous to the weld zone in flash-butt welded rail, the web of the rail has high tensile residual stresses and the head and base of the rail have compressive residual stresses. The web region is susceptible to failure since most of the weld zone of the rail is coarse grained and has porosity, inclusions and defects resulting from rapid solidification of molten metal entrapment in the weld. Efforts to reduce the amount of these tensile residual stresses require recognition of their causes. In this research, microscopic and macroscopic studies were carried out on vertical and horizontal sections of the weld zone in the head, web and base of the rail. Just after flash-butt welding, the temperature of the web between the current carrying copper electrodes is higher than the temperature of the head and base of the rail. Therefore, by cooling the weld zone to room temperature, the amount of web contraction between the electrodes is higher than the amount of base and head contraction and consequently tensile residual stresses are produced in the web at and near the weld zone. In the head and base of the rail, compressive residual stresses are developed.