This paper details the field-testing approach and results of thermite welds used in railway applications. Rail steels made from R260 grades are welded by two different processes: the standard process according to the European standards, and a recent technology. Welds are introduced in the same testing location to ensure comparable loading conditions in the aim of studying their degradation behaviours. The total testing-period is 6 months. During the in-service period, the surface hardness of the running band, in the welded area, is recurrently measured. For an accurate assessment of field results, a vehicle/track interaction (VTI) model evaluated the expected dynamic loads induced by the initial vertical irregularities. The simulations show that the highest dynamic load at the wheel/rail contact happens at the location of the maximum absolute gradient, in accordance with previous research. Particularly, dipped welds show relatively high dynamic forces inducing a high loss of the transversal profile. In respect of the field results, the comparison of initial and final surface hardness indicates a significant increase for ‘ALFONS’ welds over the welded areas. Additionally, all welds depicted a cyclic increase and decrease of the running band hardness. This result is discussed according to the ratcheting susceptibility of welds and eventual wear progression. For a testing-period of 10 weeks, the gauge corner of one ‘ALFONS’ weld developed a crack. The assessment of the longitudinal profiles revealed changes of the vertical irregularities that may modify the dynamic loads, and further the rolling contact fatigue mechanisms and degradation rates.

The aluminothermic welding (ATW) process is the most commonly used welding process for welding rails (track) in the field. The large amount of weld metal added in the ATW process may result in a wide uneven surface zone on the rail head, which may, in rare cases, lead to irregularities in wear and plastic deformation due to high dynamic wheel-rail forces as wheels pass. The present paper studies the introduction of additional forging to the ATW process, intended to reduce the width of the zone affected by the heat input, while not creating a more detrimental residual stress field. Simulations using a novel thermo-mechanical FE model of the ATW process show that addition of a forging pressure leads to a somewhat smaller width of the zone affected by heat. This is also found in a metallurgical examination, showing that this zone (weld metal and heat-affected zone) is fully pearlitic. Only marginal differences are found in the residual stress field when additional forging is applied. In both cases, large tensile residual stresses are found in the rail web at the weld. Additional forging may increase the risk of hot cracking due to an increase in plastic strains within the welded area.

This study examines the properties of stratified surface layers on rails in service and presents a hypothesis explaining their origin. The stratified layer consists of a white etching top layer and a brown sublayer. The metallurgical composition and properties of this sublayer are found to match with that of globular bainite. The occurrence of stratification in the surface layer is explained by the thermomechanical cycle for a material point on the rail surface under wheel-rail contact. Difference in the surface and subsurface cooling rates after reaching the austenitisation temperature may lead, depending on the chemical steel composition, to the generation of two different phases (martensite and bainite) and stratification. The exclusive occurrence of sandwich layers on rails that have been in service is attributed to the hardening of the top layer, leading to a reduced thermal conductivity, which gains relevance at an increasing depth. The granular morphology of the bainitic sublayer, exhibiting weak globular inclusions, facilitates the initiation and the propagation of transverse cracks, thus contributing to the development of RCF.

One of the most critical issues in railway engineering is the rail lifetime optimization. In track, rails suffer from various degradation forms like the head checks, squats and studs. The white etching layer (WEL) is considered as a primary stage of damage. The WEL usually appears as a metallurgical change due to the severe loading in the rail running band. This work addresses their generation based on the wheel-rail contact together with a metallurgical analysis. Influences of microstructure and stress on the austenite transformation kinetic are simulated. Consequently, the isothermal austenization diagrams for R260Mn, R350HT and R370CrHT grades under stress are discussed. It turns out that the austenitic transformation is possible within a comparable time to the wheel-rail contact duration.