It is reported that the Channel Tunnel between England and France is the most heavily used railway line in Europe, with annual traffic of more than 100 million tons. The heavy traffic causes rapid degradation of the rails, both in the tunnel and in the terminal loops. Studies initiated by Corus with its bainitic and MHH extra-hard heat-treated rails are aimed at increasing their life by 50%.

Eurotunnel encounters two types of problem related to rail wear. Firstly, in the tunnel, rails are affected by cracks (fatigue defects), which oblige the operator to regrind them regularly and replace them completely after 650 million tons of traffic – about every six years. Secondly, the rails in the terminal loops in France and England wear extremely rapidly because of the small radius of the track curve (between 300 and 500 metres). These lines are used by shuttles turning around to return through the tunnel in the opposite direction.

To solve these two problems, studies have been initiated, subsidised by the France. The rails sub-project is directed by Corus Rail France, partnered with Railtech for the thermit welding of rails and by INSA Lyon, which is the university institute studying wear and cracking mechanisms.

Corus has supplied rails for test areas. The first of these involves bainitic grade rails, for the tracks inside the tunnel itself. This type of steel is known in the mechanical engineering industry for its fatigue resistance, but is an innovation in the rail sector. These steels are more resistant but also more difficult to work; the bloom manufacturing processes have to be adjusted and the right chemical composition identified.

In the two terminal loops, MHH extra-hard heat-treated rails have been laid. Particularly wear-resistant, they are used for instance on heavily-loaded mine tracks. Their production is made possible by the development at the Corus plant at Hayange of a specific heat treatment procedure which avoids the need for roller straightening in the final stage. This procedure leaves an extremely low level of residual stress in the rails, which substantially reduces the risk of crack propagation in the web of the rail.

The declared objective of the study is to lengthen rail life by 50%, both in the tunnel and in the terminal loops. The MHH test rails were laid in April and September 2007. The bainitic rails were laid in January and March 2007. To date the results are on target, but the study will not be completed for another four years. The long-term commercial aim is to replace the 56km of double track in the tunnel and the 15km comprising the loops both in France and England.

About 15,000 tons of heat-treated rails have been supplied to Eurotunnel by Corus over the last four years.

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