The Effects of Service Lifetime and Duty on the Residual Stress in Railway Rails

Abstract

The effects of differing service lifetimes and conditions on the wear profiles, microstructural development, mechanical properties, and residual stress in railway rails was studied. The rail material was BS 113A grade 220, the most common grade used in the UK. A specimen of unused rail, fabricated under identical conditions, provided a control specimen against which all changes could be assessed. Careful metallographic examination, confirmed by microhardness profile measurement, showed the development of a stable, heavily deformed layer of 5 mm thickness below the rail head and gauge corner, irrespective of service lifetime. The residual stresses were measured in cross sections through the rail and on the rail head by a combination of magnetic techniques, known as MAPS [1] . The measurements showed that for rails of short service life the stresses across the whole rail head are principally compressive, balanced by tensile stresses within the body of the head. The largest compressive stresses are found at the gauge corner. However, for rails of increasing service life, there is a transition to tensile stresses in the gauge corner, accompanied by extensive gauge corner cracks. It is thought that the presence of the tensile residual stresses causes the cracks to initiate and propagate. New rails, on the other hand, had a tensile residual stress in the head, generated by the straightening process.