Speaker
Description
The development of rail transportation results in more and more passage of trains on the railtracks, which implies service conditions more conducive to the appearance of defects due to wear or cyclic fatigue. One of these defects is the ‘White Etching Layers’. These latter owe their name to the fact that it appears white on Optical Microscopy (OM) after Nital Etching, and consists of nanometric grains of ferritic structure presenting a sur saturation of carbon. The WEL formation in perlitic steels such as rail steels is known to be heterogenous, and impacted by many factors (temperature, shear levels, pressure, cycles numbers…). Even after having been extensively studied, their formation is not completely understood today, which can probably be attributed to the fact that it is difficult to reproduce the wheel/track condition at a lab scale, as it usually implies very high number of cycles with severe contact conditions (shear, pressure, speed).
This study presents a successful attempt to reproduce White Etching Layer (WEL) under pure mechanical conditions, with the use of a new experimental test bench with tests conditions representative of the wheel-rail contact.
First, a tribological analysis of the effect of the surface preparation on material flows in the contact, hardness evolution, and formation of WEL will be presented. Then the formation mechanism of such mechanically formed WEL will be explained using a multiscale characterization approach that combines optical microscopy, scanning electron microscopy and near surface EBSD observations at the sub-µm level.
The different scenarios of the wear behavior and microstructural transformation were drawn. The study reveals that the presence of a run-in or corrosive fuse layer at the rail surface has a great effect on the microstructure evolution. This layer prevents wear and allows microstructural transformation of rail steel.
| Speaker Country | France |
|---|