Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation.

The wear behavior of two steels for tread-braked wheels (ER7⁺ and CLASS B⁺) against the same brake block cast iron was studied through pin-on-disc tests to understand the phenomena at the interface and compare the steels. The contact stress (0.61 MPa) and the sliding speeds (0.52 and 0.62 m/s) were set considering the UIC 510-5 (E) for technical approval of monobloc wheels. The friction coefficient, the weight loss of both steel pin and cast iron disc and the pin hardness were correlated with the damage of the pin. In addition, a preliminary thermal finite element model was proposed to predict the temperature of the pin contact surface. The experiments showed that a material transfer phenomenon from the cast iron disc to the steel pin and the subsequent detachment of the adhesion joints caused high friction coefficient fluctuations. The removal of the adhesion joints probably promoted the detachment of steel particles from the pin, which could explain the high weight loss and remarkable delaminations of the pin in some of the studied conditions. On the contrary, small friction coefficient fluctuations and red oxide formation due to the temperature increase were detected when the material transfer was very limited. ER7⁺ steel showed lower weight loss and less damage than CLASS B⁺ at the lowest sliding speed, the contrary was observed at the highest sliding speed. Finally, the simulation showed that the maximum temperature of the pin contact surface varies between 61 and 97 °C, which is consistent with the red oxide presence.

The diffusion of brake-shoe system has made it necessary to study brake–wheel–rail interactions. This study aims to elucidate this topic with an innovative small-scale test rig, the ‘4-contact machine’. A test procedure is designed in which an ER7 steel wheel is coupled with a R260 steel rail and two different brake-shoe materials (cast iron and sintered material). The results show that the 4-contact machine reproduces the effects of wheel–rail–brake shoe contact and damage similar to those observed on a railway wheel at the end of its life, highlighting marked differences in behaviour between the two brake materials.

Wheel microstructure significantly affects railway wheel performances. Although wheel microstructure traditionally consists of pearlite-ferrite, it is possible to detect some intermediate structures traces, for instance bainite, generated during the thermal treatment process. The difference in mechanical properties between pearlite and bainite causes stress and strain incompatibilities at their interface, and this gives rises to early crack initiation and propagation. This paper aims at investigating the presence of bainitic traces in a ferritic-pearlitic microstructure of a railway wheel through semi-analytical and numerical finite element simulations. The effect of bainitic spot shape, dimension and distribution is studied as well as stress and plastic strain in the proximity of the heterogeneities is analysed. The radius-interaxis ratio parameter, defined as the ratio between the bainitic spots radiuses and the distance between two neighbouring spots centres, is introduced to study the effect of circular-sectioned bainitic spots on the steel plasticity. It is observed that the bainitic traces form regions subjected to overstress and overstrain in the ferritic-pearlitic matrix and that the area of the bainitic spots influences the size of these regions. The bainitic spot distribution is found out to increase further the overstrain in case the radius/interaxis ratio is higher than 0.2, corresponding to about 11% of bainite in the ferritic-pearlitic matrix. Beyond this threshold value, bainite traces can compromise both RCF and wear response.