Metallographical investigation of white etching layers on railway lines

Microstructural changes on the surfaces of a number of railway lines in service for a number of years were investigated using optical light microscopy, micro-hardness measurements and TEM. Unequivocally areas were identified containing so-called "white etching layers", the hardness of which was almost twice that of the pearlitic parent steel. The TEM investigations indicated that the pearlite colonies had been dissolved just beneath the surface of the rails as a result of very heavy plastic deformation, forming a nano-crystalline microstructure of ferrite containing small amounts of cementite. In one case signs of a partial transformation of the nano-crystalline microstructure to martensite were observed.