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

Lead Research Organisation: University of Huddersfield
Department Name: Sch of Computing and Engineering

Abstract

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,

Planned Impact

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.

Publications

10 25 50
 
Description The key achievements from the research project can be summarised as follows:
1. The damage susceptibility of different track sections has been assessed using detailed vehicle dynamics and rail damage modelling to formulate guidelines for deployment of different rail steels. This has resulted in a development of a rail damage susceptibility map for a number of routes and the methodology to generate these maps.
2. A laboratory twin-disc facility has been developed that generates wheel-rail contact conditions that have a closer resemblance to the actual damaging loading conditions seen on track. It is hoped that this test rig form a useful tool for the characterisation of the next generation of rail steels.
3. Detailed metallurgical examination combined with neural network analysis of test results from selected laboratory twin disc test samples has drawn some key breakthroughs in understanding the influence of alloying elements and hardness on degradation of rail steel microstructures. This assessment was completed on a limited number of available samples, tested for RCF resistance on the small-scale twin disc machine located at British Steel, and despite this limitation the research has identified that fragmentation of the pearlitic cementite lamellae and consequently their dissolution during local plastic deformation, is a key microstructural feature differentiating the RCF resistance of steels. Steels alloyed with silicon (as is the case for HP335) resist better the dissolution of cementite, and thereby impart improved resistance to RCF. Vanadium alloyed steels, such as HP335, displayed less plastic deformation and shallower depths of cementite fragmentation than those without vanadium at similar levels hardness.
4. A detailed cost-benefit analysis approach was developed to assess the impact of optimum rail steel grade selection on whole routes. This approach includes a life cycle cost assessment using the industry-standard VTISM tool.
5. In collaboration with Network Rail, the research is 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.
A number of areas of further work have been identified through the research which will now be further investigated as part of a follow-on project commissioned by Network Rail as part of the EU Shift2Rail project, In2Track. These include:
• Verification of the research outputs through further twin disc testing and examination of in-service rail samples.
• Assessment of the depth of cementite fragmentation in both hypo and hypereutectoid steel rails taken out of track also needs to be undertaken.
• Application of the findings of the current research to the optimisation of material selection for switches and crossing. This will complement the detailed modelling work that has already been undertaken to predict the variation in wheel-rail forces and damage susceptibility of different S&C components during previous EU Shift2Rail projects.
• The influence of decarburisation on the early initiation of RCF cracks with little subsequent propagation in HP335 steel needs to be examined since there is no objective measure.
Exploitation Route The key findings from the research will be used to develop guidance on the deployment of available rail steels to reduce rail damage and therefore whole life costs. This guidance should be disseminated to infrastructure maintainers and track engineers so that rail networks can benefit from the research.
The techniques investigated to assess microstructure response, and the experimental data from testing current rail steel, can be used to characterise the performance of new steels developed by rail steel manufacturers in the future.
The developed modelling techniques applied for the assessment rail damage susceptibility will be used to support future research into wheel-rail damage and outputs published in future conferences/journal papers.
Sectors Manufacturing, including Industrial Biotechology,Transport

 
Description The detailed metallurgical examinations and neural network analysis completed during the research has produced some key breakthroughs in understanding the influence of alloying elements and hardness on the degradation of rail steel microstructures. This has resulting in the publication of three journal articles and the outputs have been further refined during a follow-on project recently commissioned by Network Rail to support the EU Shift2Rail project, In2Track (http://projects.shift2rail.org/s2r_ip3_n.aspx?p=IN2TRACK). A laboratory twin-disc facility has been developed during the research that generates wheel-rail contact conditions that have a closer resemblance to the actual damaging loading conditions seen on track. This test rig will support the future characterisation of current and next generation of rail steels, along with the performance of rail welds and materials for switches and crossings (S&C). This test rig has been utilised during the follow-on project (see above) and there has also been interest from a number of rail manufacturers in using the test rig for further research and development. A detailed cost-benefit analysis (CBA) has been undertaken to assess the cost impact of optimum rail steel grade selection of whole railway routes. This included the novel application of the UK industry-standard strategic cost modelling tool VTISM. The developed methodology has gained interest from international infrastructure managers and has recently been presented to participants of the 'International Collaborative Research Initiative' (ICRI) into RCF and wear of wheels and rails being coordinated by National Research Centre of Canada (http://icri-rcf.org/). The outputs from the CBA have also helped to quantify the benefits of current Network Rail strategy for the deployment of HP335 rail steel grade (e.g. in critical curves where RCF and wear causes the premature replacement of the rail, in moderate curves to preserve the ground rail profiles and increase the rails resistance to RCF and in tight curves with high rates of wear, where there is a cost savings and operational benefits from applying HP rail across the whole route). The research on cost-quality interactions was included in a bid to the Northern Rail Innovation Fund (provisionally approved in 2017), and that new research on the complex interactions between cost and quality on the railways was undertaken, taking account of both predictive and reactive maintenance aspects. This work built on research in the energy and health areas. An article in the IMechE Journal of Rail and Rapid Transit has recently been published which summaries the techniques developed for the deployment of available rail steels to reduce life cycle costs. Network Rail are currently utilising the research outputs to develop enhanced guidelines Route Asset Managers (RAMs) to support the optimum selection of rail steels taking into account damage susceptibility, vehicle-track characteristics, operational conditions and economic benefits.
Sector Manufacturing, including Industrial Biotechology,Transport
Impact Types Economic,Policy & public services

 
Description Guidance for Rail Grade Selection
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Impact In collaboration with Network Rail, the research is 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. Part of the Vehicle/Track System Interface Committee's strategic objectives is to (a) reduce the 'stress state' and (b) increase the stress tolerance of rails. Introduction of alternative rail grades can help to combat wear and RCF damage, increasing 'stress tolerance' of system and improving rail management strategy. To achieve this good guidance for designers and track engineers is required for selecting appropriate rail grade for a given situation (e.g. track curvature, cant deficiency, vehicle type (PYS)). Tools such as 'Track-Ex' can be used (and are currently being more widely used in new designs), but more general guidance would be useful which does not require detailed modelling.
 
Description In2Track (Linked Third Party Agreement)
Amount £84,000 (GBP)
Organisation Network Rail Ltd 
Sector Private
Country United Kingdom
Start 03/2018 
End 02/2019
 
Title Rail steels performance data 
Description Results from historical and current twin disc tests have been correlated and combined in a single database. This database will be used to characterise the performance of future rail steels developed by rail manufacturers and support the development of rail damage models. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Database provides a singularly unique dataset for the industry, with test results full matrix of rail steels. 
 
Description Wheel-rail wear mapping 
Organisation University of Sheffield
Department School of Clinical Dentistry Sheffield
Country United Kingdom 
Sector Academic/University 
PI Contribution Wheel-rail contact modelling, conducted to support the development of a rail damage susceptibility map during the current award, has also provided useful outputs to support the future improvements to wear maps used in wheel-rail wear modelling. This data have provided information on typical contact conditions generated at the wheel-rail interface, including: size, shape and load, and identifies areas of the wear map where additional experimental / test data is required.
Collaborator Contribution University of Sheffield is collating wheel-rail contact and wear data to support the future development of wear maps. These wear maps will allow us to reduce some of the assumptions / inaccuracies in the modelling of wheel-rail wear. This collaboration forms part of the International Collaborative Research Initiative (ICRI) into RCF and Wear of Wheels and Rails and includes contributions from a number of international participants.
Impact Presentations at National and International seminars organised by the ICRI.
Start Year 2016
 
Description Industrial forum on extreme environment materials and coatings 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The event included invited talks from academia and supply-chain leaders describing the latest achievements and key challenges in the field of materials and coating in challenging environments. The EPSRC research project was presented during the second session and identified the key challenges in the rail industry, related to rail steels, and identified potential future collaborations to meet these challenges.
Year(s) Of Engagement Activity 2016
URL http://www.hud.ac.uk/research/researchcentres/materials/events/conferences/eemc/
 
Description International Collaborative Research Initiative - RCF and Wear of Wheels and Rails 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited to present initial outputs from the research at second UK ICRI workshop in London. This was also broadcast via WebEx to delegates internationally.
Year(s) Of Engagement Activity 2017
URL http://icri-rcf.org/downloads.php
 
Description Rail Research UK Association Annual Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Conference presentation on the Deployment of Available Rail Steels to Reduce Life Cycle Costs. Conference paper also selected for inclusion in a special issue of the IMechE Journal of Rail and Rapid Transit. This paper was submitted in January 2018.
Year(s) Of Engagement Activity 2017
URL https://www.railengineer.uk/2018/01/17/rruka-annual-conference-2017/
 
Description Rail Steels Research Steering Group 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Presentation of the research progress and initial outcomes to a steering group set up specifically to provide industry guidance to the research project. Participation from key industry groups, including: Network Rail, British Steel, Rail Safety and Standards Board.
Year(s) Of Engagement Activity 2016
 
Description Vehicle/Track System Interface Committee 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited to present the aims/objectives and initial findings of the research to the key railway industry stakeholder group the "Vehicle/Track System Interface Committee", hosted by the Rail Safety and Standards Board.
The presentation stimulated considerable discussion on the research topic and highlighted the potential impact of the research to the industry.
Potential follow on projects were discussed and support obtained from the stakeholder group.
Year(s) Of Engagement Activity 2017
URL https://www.rssb.co.uk/groups-and-committees/rssb-board/technical-strategy/technical-leadership-grou...
 
Description Vehicle/Track System Interface Committee Annual Seminar 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Invited to present the background, methodology and outputs from the research award to potential industry end users. This was followed by a presentation from Network Rail on selection of optimum rail steels which uses some of the results from this research to develop guidance for rail steel grade selection.
Year(s) Of Engagement Activity 2017
URL https://www.railengineer.uk/2018/01/18/improving-the-vehicle-track-interface/