The potential for suppressing rail defect growth through tailoring rail thermo-mechanical properties

Thermal damage of rails can occur through brake lock-up, or traction control system failure to prevent wheel spin. In most cases the damage produced is shallow and takes the form of a "white etching layer", usually thought to have a martensitic structure, formed as the steel is heated above its eutectoid temperature and then rapidly cooled as the wheel moves away. In many cases such layers are benign, but there is evidence of crack initiation at their interface with the sub-surface layers of the rail in “stud” defects. The metallurgical transformation during the formation of white etching layers leads to a volume change for the steel, leaving not only a transformed microstructure, but also locked-in stress. The influence of this additional locked-in stress on development of an initiated crack is studied in this paper, and the work extended to consider how alternative materials which react differently to the thermal input may offer a means to suppress crack development through locking in beneficial rather than problematic stresses.