Effect of local induction heat treatment on the induced residual stresses in the web region of a welded rail

Abstract

Rails are often joined by welding and about 80–90 per cent of tracks are welded using the flash-butt welding method. As the result of the welding process, high tensile residual stresses are induced in the web region of the rail, at and near the welded zone. Since the main part of the welded zone is coarse grained and has porosities and inclusions, the web part of the rail is susceptible to failure. The magnitude of the induced stresses may be reduced by stress-relieving heat treatment, but in practice the heat treatment process is not used as it is very time consuming and adds to overall project costs. In this paper, microscopic studies were performed on the welded zone in the head, the web and the base parts of the rail. The effects of local induction heat treatments on the microstructure and on the resultant tensile residual stresses in the web region were studied. To do this, firstly, dilatometery specimens were prepared from the base metal of the rail. These were heat-treated under different induction heat treatment cycles and the resulting phase transformation and the changes in the length of the specimens were obtained. Secondly, the effects of local induction heat treatments on the residual stress field in the welded zone of the rail were investigated using finite element analysis. Finally, a local induction hardening and tempering heat treatment is proposed to reduce the residual stresses in the web region of a welded rail.