An evaluation of fatigue crack growth and fracture toughness characteristics in rail steels.

Abstract

In order to evaluate the fatigue fracture and the fracture toughness characteristics of rail steels, an axial residual stress determination, fatigue crack growth test, static and dynamic fracture toughness tests of samples from rails and the three point bending fatigue test of a full rail head were studied for six rail steels which differed in composition and processing histories. The rails consisted of a standard carbon rail, a full heat-treated rail, two Cr-Mo rails, a Cr-V rail and a head-hardened rail. All other rails except the head hardened rail had tensile residual stress in both sides of the head and the base, but the head-hardened rail had high compressive residual stress in the head which seemed to be desirable for fatigue and fracture toughness resistance. The head-hardened rail exhibited a high level of threshold and fatigue fracture toughness in the fatigue crack growth test, high static fracture toughness resistance and high fatigue resistance in the full rail head test. On the other hand, the Cr-V rail exhibited the most inferior characteristics in all tests. The fracture toughness values from all tests had the tendency to increase with an increase in the tensile ductility of each rail steel.