The role of microstructure and its stability in performance of wheels in heavy haul service

Abstract

Thermal or thermo-mechanical loading is one of the major causes of wheel surface damage in Australian heavy haul operations. In addition, multi-wear wheels appear to be particularly sensitive to thermo-mechanical damage during their first service life. Such damage can incur heavy machining penalties or even premature scrapping of wheels. The combination of high contact stresses as well as substantial thermal loading (such as during prolonged periods of tread braking) can lead to severe plastic deformation, thermal fatigue and microstructural deterioration. For some high-strength wheel grades, the increased sensitivity to thermo-mechanical damage observed during the first service period may be attributed to the presence of a near-surface region in which the microstructure is more sensitive to these loading conditions than the underlying material. The standards applicable to wheels used in Australian heavy haul operations are based on the Association of American Railroads (AAR) specification M-107/M-208, which does not include any requirements for microstructure. The implementation of acceptance criteria for the microstructure, in particular that in the near-surface region of the wheel, may be necessary when new wheels are purchased. The stability of wheel microstructures during thermo-mechanical loading and the effects of alloying elements commonly used in wheel manufacturing are reviewed. A brief guide to improving thermal/mechanical stability of the microstructure is also provided.

Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysis

“…The stability of wheel microstructures during thermomechanical loading and the effects of alloying elements commonly used in wheel manufacturing were studied [30]. They stated that pearlite and bainite have different strain hardening characteristics (i. e. a mechanical property mismatch) which may cause high local strain or stresses at the phase interface that contribute to crack initiation and propagation [34]. This is similar to the situation of acicular ferrite-bainite which was obtained in this at higher reliability values.…”

Numerical study about the effect of bainitic traces on plasticity in ferritic-pearlitic railway wheels

“…Experimental evidence showed that localised deformation may easily lead to the initiation of fatigue cracks and that the less resistant region at the boundary between ferritepearlite and bainite may become the preferential path of the cracks, causing for example the decohesion at the interface and the spalling failure of the wheel. 28,30,53 The results of the finite element simulations showed that the plasticised area is affected by the bainitic spot size (the bigger the spot, the larger the overstrained area). However, the spot size does not influence the order of magnitude of the plastic strain.…”

“…Experimental evidence showed that localised deformation may easily lead to the initiation of fatigue cracks and that the less resistant region at the boundary between ferrite-pearlite and bainite may become the preferential path of the cracks, causing for example the decohesion at the interface and the spalling failure of the wheel. 28,30,53…”

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.…”