Microstructural investigation of white etching layer on pearlite steel rail

The microstructure of the white etching layer (WEL) on the contact surface of a head-hardened pearlitic rail was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a three-dimensional atom probe (3DAP). The WEL was confirmed to be composed of severely deformed pearlite lamellae as well as nanocrystalline martensite, austenite and cementite. The carbon atoms in the topmost surface of the WEL were distributed nearly uniformly. A few atomic percent of carbon was dissolved in the ferrite of the deformed pearlite lamellae. The maximum hardness was observed in the deformed pearlite region within the WEL rather than on the topmost surface layer. The microstructural feature of the WEL and the reason why the deformed layer shows a white contrast in optical microscopy are discussed.