The railway network is always looking for ways to reduce costs and improve efficiency. This includes minimising the wear and tear to its trains and tracks, in particular reducing the forces generated between the train wheels and the track.
The Institute of Railway Research has carried out extensive research in this area working closely with the rail industry. Increasing asset life and reducing maintenance contributes to increased service availability and reliability for rail passengers. Selecting the right materials for wheels and rails is a complex task with many conflicting requirements, including a range of failure mechanisms, operating conditions and the associated financial implications.
Recent research has focused on investigating changes to vehicle-track characteristics, such as wheel profile design, suspension design and the way in which the vehicle responds to track conditions. However, there has been less research on increasing the resistance of the materials to the imposed forces.
EPSRC funded research
The EPSRC (Engineering & Physical Sciences Research Council), in cooperation with RSSB (Rail Safety and Standards Board) and DfT (Department for Transport), have funded a research project led by the Institute of Railway Research at the University of Huddersfield in collaboration with the University of Cambridge, University of Leeds and Cranfield University. The industrial project stakeholders and members of the steering group included British Steel, Network Rail and RSSB.
Phase 1 of this research project aimed to establish a comprehensive scientific understanding of the metallurgical characteristics of rail steels. This will enable scientifically-informed choices, which take into account both the specific requirements arising from the peculiarities of railway wheel-rail contact and the economic trade-offs at a system-wide level.
The results of this research will help establish the future design rules to engineer steel microstructures that provide a step change in the resistance to key degradation mechanisms with greater predictability of the deterioration rates.
Historically the rail industry has relied upon the testing of properties such as hardness and tensile strength and to a limited extent comparative assessment of wear resistance under simplified contact conditions. However, there is a knowledge gap in the understanding of the influence of microstructural constituents of various steels on their ability to effectively resist other damage mechanisms such as rolling contact fatigue (RCF), plastic deformation and corrugation.
High performance rail steel
Recent developments of ‘High Performance’ (HP) rail steels have shown, through laboratory and on-track testing, that improvements in the resistance to both wear and RCF can be achieved through the right choice of alloying elements to alter the microstructural characteristic of the steel. This includes HP335 rail, developed in the UK by British Steel (formerly Tata Steel) and successfully deployed by National Rail, and carbide-free bainite steels deployed in Eurotunnel. However, the understanding of the reasons for the success of such steels requires further fundamental research.
Phase 1 of the research project has made some key breakthroughs in understanding the influence of alloying element and hardness on degradation of rail steel microstructures. In collaboration with Network Rail, the research is also supporting the development of guidelines to optimise the selection of rail steel grades taking into account damage susceptibility, vehicle-track characteristics, operational conditions and economic benefits.
Discussions are currently on going with the industrial project stakeholders in relation to funding Phase 2 of the research which proposes to extend the experimental testing and microstructural assessment to cover a wider range of rail steels.