The background
Ever wondered what happens as that tram passes through your city centre, taking people to their workplaces, homes or wherever it is they want to go? The tramway often shares its route with road vehicles and its rails are, therefore, embedded in the road surface. As it winds its way through the city, the wear and tear is acute, especially where there are steep gradients and tight curves.

 

Replacing the embedded track poses a complex challenge to light-rail infrastructure managers: besides the high cost of excavation, there is also disruption to road traffic sharing the route. The solution — as envisaged by Tata Steel’s Europe operations — lies in a premium grade grooved rail that is designed to extend the track’s serviceable life, provide increased resistance to wear-and-contact fatigue, and also be restorable by welding.

 

The innovation
The team at Tata Steel’s Europe operations set out with the idea of creating a harder rail steel that could be repaired through welding and, thereby, have a longer usage period. The result was the 330V, which has a wear resistance above that of anything available in the market and is compatible with Tata Steel’s patented high-integrity weld-repair process.

 

The 330V, which the company has patented, addresses the customer requirement for a premium product to be used on the tight radius corners that are required for trams in an urban environment.

 

Modern rail steels, typically, have a fully pearlitic microstructure, comprising layers of a ‘hard’ cementite phase and a ‘soft’ ferrite phase. Traditionally, the properties of the rail are modified by alloy additions, giving added solution strengthening to the ferrite, or by additional heat treatment processing to refine the pearlite layer thickness.

 

The first novel step in the 330V development is the precipitation hardening of the ferrite layers. Precise levels of vanadium are added; these precipitate as vanadium carbides in the ferrite matrix, resulting in higher wear and rolling contact fatigue resistance than is possible through solid solution strengthening alone.

 

The 330V is a premium-grade steel which, unlike heat-treated premium grades, is weld-restorable in service. Levels of carbon and other alloying additions are carefully chosen and controlled, such that the martensite start-and-finish temperatures allow a robust weld deposit to be applied to the gauge corner, in line with Tata Steel’s patented weld-restoration procedure.

 

This composition is the only rail steel in the market that offers first-life performance that is the equivalent of the best available heat-treated product, as well as the weld-reparability of standard grade. This allows a worn rail to be restored to its original profile (rather than have it be replaced).

 

Compared with downstream heat-treatment processing, which requires an additional plant and incurs additional cost, the 330V achieves these premium properties in the ‘as-rolled’ condition through the intelligent design of chemical composition.

 

The payoff
The development of 330V allows Tata Steel’s Europe operations to overcome the competitive disadvantage it faced vis-a-vis its rival Voest Alpine on wear-and-contact fatigue resistance, and to create a unique selling point of a weld-repairable premium grade rail.

 

Increasing the serviceable life of grooved rail and reducing the frequency of replacement provide significant financial benefit to the network operator, since the cost of rail only makes up a fraction of the cost of replacement (less than 10 percent).

 

The market price for rival heat-treated rail is 10-15 percent above standard grade based on first-life benefits. Since weld restoration helps it achieve multiple lives, the 330V offers considerable additional value over competing products.

 

Lengths of 330V rail are now with some of the company’s light-rail customers and awaiting installation at the trial sites of Sheffield Supertram, the Brussels Metro and French tramways in Paris and Strasbourg. These are expected to be installed in 2012.

 

The demand for such a premium product is expected to increase Tata Steel’s market share in this segment from 25 percent to 50 percent by 2016, generating an additional £1 million in profits every year.