Designing steel composition and microstructure to better resist degradation during wheel-rail contact

To reduce whole-life costs of the railway system (through increased asset life, reduced maintenance) and generate performance improvements (such as increased service availability and reliability), it is important to select the optimum material composition for railway components. Selecting the optimum materials for wheels and rails is a complex task with many conflicting requirements, including: a range of failures mechanisms, variety of operating and loading conditions and the associated financial implications. This research will establish a comprehensive scientific understanding of the metallurgical characteristics of rail and wheel steels to enable scientifically-informed choices. It will take account of both the specific requirements arising from the peculiarities of railway wheel-rail contact and the economic trade-offs at a system-wide level.

Recent development of 'High Performance' (HPRail) rail steel by Tata Steel has shown that improvements in the resistance to both wear and rolling contact fatigue (RCF) can be achieved through judicious choice of alloying elements to alter the microstructural characteristic of the steel. However, the understanding of reasons for the success of such steels requires further fundamental research to establish how the different constituents of steel microstructures react to the forces imposed at the wheel-rail interface. The results of such research will help establish the 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.

The project combines the skills of an interdisciplinary team from four Universities (based at the Universities of Huddersfield, Cambridge, Leeds and Cranfield), necessary to deal with the complexity of the phenomena,

This research will establish a comprehensive scientific understanding of the metallurgical characteristics of rail and wheel steels to enable scientifically-informed choices. It will take account of both the specific requirements arising from the peculiarities of railway wheel-rail contact and the economic trade-offs at a system-wide level. The key deliverables from the proposed research are as follows:

1. Guidelines for the optimum deployment of current rail steels in appropriate locations within a rail network to minimise life cycle costs
2. Design criteria for next generation of rail steels based on key degradation mechanisms, operating conditions and economic benefits
3. Economic model for use by infrastructure managers and regulatory bodies for assessment of budgetary requirements

These deliverables will have wide ranging benefits to the rail industry with significant impact in key areas for rail users and suppliers.

HP rail developed in the UK is currently being deployed by Network Rail, but wider acceptance requires further fundamental scientific and economic validation. This will be delivered during the proposed project. Rail manufacturers have developed a variety of new bainitic steels; if a design criterion was better defined the introduction and take-up of these new rail steels would be easier to implement and at lower economic costs. The European standard also currently defines a range of 9 pearlitic steels with varying levels of rail hardness, whereas it is the steel microstructure - which is the focus of this research project - that governs the damage resistance of the rail steel. Life cycle costing has been attempting in various projects, but the granularity of these assessments is not representative of the damage experienced. The model proposed during this research will take into account the granularity of the network, based on: susceptibility to degradation, vehicle-track operating conditions, safety and risk.

Thus the research addresses some of the challenges defined in the current Rail Technical Strategy and suggests that the research could have a significant impact on the rail industry in Britain. From the perspective of the tax payer, in 2013/14 the government provided £3.5bn of direct support to Network Rail, and Network Rail is targeted over the next five years with efficiency targets of 16% and 20% for maintenance and renewals respectively. In 2013, track maintenance and renewals (M&R), which is the focus of this project, accounted for just over one third of total M&R costs, or around £1.3bn per year in monetary terms. Thus, this project has considerable scope to reduce costs and deliver benefits to tax payers and, to the extent that lower costs are passed on, also to passenger and freight users. Users could also benefit through a reduction in train disruptions, improved service, and environmental impact.