Friction modifiers effects on tribological behaviour of bainitic rail steels

Abstract

Bainitic steels are gaining popularity for application in the railway switches and crossing, thanks to their better rolling contact fatigue (RCF) and wear resistance. The rail degradation caused by RCF and wear could be also reduced by the use of friction modifiers (FM) through their ability to reduce the lateral load during wheel passage. This paper presents the microstructure and the mechanical properties of newly designed bainitic steel grades; B1400+ and Cr-B potential candidates for switches and turnouts railroad industry. It investigates their friction and wear performances using the HOrizontal twin DIsk Machine. The tribological behavior is evaluated under dry and lubricated conditions in combination with three commercial friction modifiers. Results show a better wear resistance of Cr-B steel in case of abrasive mechanism that dominates the dry experiments. This work defines the efficiency of FM as a low and stable friction coefficient concomitant to a low wear rate. It appears that a good tribological performance is untimely linked to the chemical composition of the friction modifier. In case of lubricated contact, cross-sectioning of wear scare confirms the generation of an interfacial layers. These layers have an impact on the wear mechanism and debris detachment susceptibilities of bainitic steels.

Rheological and tribological evaluation of friction modifiers for wheel‐rail applications

“…FM's can also be analysed as a suspension that usually presents a microstructure of particles with additional properties to improve performance. The relevant parameters for the film formation are the composition of the FM (suspension), the rheology properties, the detached wear debris, and the chemical affinities of the metallic surfaces 5 …”

“…By studying its rheological properties, the evaluation of FM for wheel‐rail systems has been hampered by the complexity of measurements under real‐world conditions. In the literature, some approaches seek to predict the behaviour of the rheology of the third body or layer 3,5 . The response to shear stress and shear rate plays an essential role in understanding FM's properties in extreme conditions such as a wheel‐rail system.…”

“…Even though rheological tests provide essential information to understand the FM's behaviour, the parameters' values used in the laboratory are not comparable to those observed in the field. In that case, several authors have used and preferred tribological tests to mitigate this uncertainty 5 . In this paper, both approaches are put together to evaluate different commercial and custom‐made FM's.…”

“…In liquid or semi-liquid lubricants, typically, the amount of base oil in a commercial product varies from 80% to 85% 4 with the addition of 15%-20% of solids to improve wear resistance. 5 In the case of solid lubricants, the most frequently used is Molybdenum disulfide (MoS 2 ) which is a well-recognised solid lubricant. MoS 2 is useful in the boundary lubrication regime in order to prevent wear where metal to metal contact exists.…”

Dry Rolling/Sliding Wear of Bainitic Rail Steels under Different Contact Stresses and Slip Ratios

“…As for the bainitic steel, several studies mainly focused on the comparison of the wear resistance [ 14 , 15 , 16 , 17 , 18 , 19 ] and RCF [ 3 , 15 , 16 , 20 ] between bainitic steels and pearlitic steels under the same working condition. However, the results were very contradictory.…”