Steels for rail axles - an overview

The comparative assessments and an overview of mechanical, chemical, and physical properties of rail axles are presented. This review focused on the effects of compositions and microstructure on fatigue, fretting and corrosion fatigue of rail axles. The two main steel grades: low carbon steels for commuter trains and high strength low alloy steels for high-speed trains have ferrite-pearlite microstructures with 20–40 µm ferrite grain sizes. Minimum allowable yield and ultimate tensile strengths are 330 MPa and 600 MPa, and the minimum longitudinal and transverse toughnesses are 35 J and 22 J. Most axle failures are associated with surface and sub-surface defects with micro-cracks nucleating from ballast (small-sized pebbles in rail tracks), minute oscillatory movement leading to fretting, microstructural inclusions, and corrosion pits. The implications for structural integrity are highlighted and areas for future research directions are highlighted.