Figure 1: (extract from [5]) (a) macroscopic view on the tread of a rail (S54/900A steel) showing TSTs or “White Etching Layer.” (b) Transverse cross-section of the upper part of a rail (a). The parent phase (grey part) is pearlite, which still remains in the rail when TSTs have developed and the daughter phase (white part), occurring at the surface, is “quasi-martensite.”