Influence of environmental conditions and oxidation on the coefficient of friction using microalloyed rail steels

Abstract

In railway systems, certain atmospheric conditions – mainly related to temperature and relative humidity – lead to the creation of iron oxides which can affect the coefficient of friction between the wheel and the rail. This can result in increased wear of the rail, reducing its service life and thus increasing replacement costs. Pin-on-disc tests were conducted in a climate chamber to study the influence of environmental conditions and iron oxides on the coefficient of friction. The iron oxides generated on the surface of specimens extracted from microalloyed rail steel during wear tests were analysed using X-ray diffraction. The results show that hematite (α-Fe2O3) is the predominant iron oxide among all the oxides generated on the worn surfaces. It was further noted that the oxide layer resulting from the rise in both temperature and relative humidity does not significantly affect the average coefficient of friction for each steel samples tested. High relative humidity combined with high temperature leads to the formation of α-Fe2O3, which tends to increase the coefficient of friction. However, a boundary lubrication effect is observed at higher relative humidity due to a condensed water film, which reduces the coefficient of friction and counteracts the increase of the coefficient of friction expected due to the presence of hematite.

Use of synthetic Fe3O4-rich tribofilms to investigate the effect of microconstituents, temperature and atmosphere on the friction coefficient during pin-on-disc tribotest

“…Kempla et al [47] showed that the CoF of hematite (∼0.65) is always higher than the CoF of magnetite (∼0.55). Other works also associated the presence of ɑ-Fe 2 O 3 with increased CoF compared to Fe 3 O 4 and γ-Fe 2 O 3 , maghemite [48,49], which are part of the successive oxidation reactions of iron [50][51][52][53]. Kato and Komai [6] showed that adding exogenous oxide nanoparticles, such as CuO, induces a severe-to-mild wear transition due to the formation of a protective tribofilm during pin-on-disc tribotest, decreasing wear and friction.…”

Examining Wear Mechanisms in Railway Wheel Steels: Experimental Insights and Predictive Mapping

“…Wear is affected by several phenomena, such as shear stress at the contact [35,36], wheel material (hardness and microstructure) [10,[37][38][39][40][41][42][43][44][45][46], lubricants and debris [47][48][49], temperature [50][51][52][53][54], polygonization [55][56][57][58][59], and surface treatments [60][61][62][63][64]. In actual wheels, polygonization is caused by wheel-rail coupled vibration, and material loss is a result of the wheel-rail coupled vibration.…”