Crack formation within a Hadfield manganese steel crossing nose

Switches and crossings in rail networks suffer from complex loading which may induce severe damage and defects, including formation of cracks that can result in rail breakage. This paper focuses on the microstructure and crack network in a damaged Hadfield manganese steel crossing nose. The extent of deformation has been quantified by hardness measurements, optical microscopy and scanning electron microscopy (SEM) including electron back scattering diffraction (EBSD). It is found that the wheel contact causes high deformation hardness of over 600 HV, around three times that of the base material, and the strain hardening extends up to a depth of about 10 mm from the running surface. Microscopy indicates the deformation microstructure is composed of bands of both deformation twins and deformation induced dislocation boundaries. The complex crack network within the nose of the crossing has been investigated using 3D X-ray tomography, where both surface and subsurface cracks are detected with the majority of the cracks originating from the surface. The crack network has been related to the observed deformation microstructure and it has been found that although the hardening and the deformation of the Hadfield manganese steel is quite different from that of commonly used pearlitic rail steels, the crack morphologies are found to be quite similar for the two materials.