Metallographical investigation of white etching layers on railway lines

Microstructural changes on the surfaces of a number of railway lines in ser vice 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 almo st twice that of the pearlitic parent steel. The TEM investigations indicat ed that the pearlite colonies had been dissolved just beneath the surface o f the rails as a result of very heavy plastic deformation, forming a nano-c rystalline microstructure of ferrite containing small amounts of cementite. In one case signs of a partial transformation of the nano-crystalline micr ostructure to martensite were observed.