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British Steel alloy makes tough tracks

A new steel alloy for railway tracks promises to be tougher and more resistant to fatigue than traditional materials -- but less hard wearing on rolling-stock wheels.

The alloy, which has had patents applied for in 40 countries, was developed by Cambridge University researcher Dr Harry Bhadeshia and British Steel, and is now undergoing extensive trials on a test track using heavy axle loads ranging from 25 to 66 tonnes.

Steel for conventional rails relies on microstructures which contain carbides -- compounds of iron and carbon. Though hard and wear-resistant, these rails are brittle. The new steel contains no carbides and is silicon-rich, giving a radically different microstructure.

Dr Bhadeshia explained that the new alloy came about as a result of a talk he gave to British Steel in 1989 on the subject of a particular property of steel which he had been studying for some years. After the talk he was asked by Dr Vijay Jerath, of British Steel, if his research could be applied to steels for rails.

A Reader in the Materials Science and Metallurgy Department at Cambridge, Dr Bhadeshia has received support for his basic research into metals and alloys, especially steel, from EPSRC and its predecessor, the Science and Engineering Research Council (SERC).

Back in the laboratory a computer and phase transformation theory were used to model three alloys for British Steel, based on three criteria -- strength, wear resistance and toughness.

A crucial element of the new alloy is the crystal structure bainite, which is a product of phase structure transformation, but it is not clear under what conditions it grows. To calculate the growth it is important to understand the atomic mechanisms. "For a long time I have been doing basic research into the atomic mechanisms by which bainite forms. This is the reason why we were able to do the calculations quickly," Dr Bhadeshia said.

British Steel -- one of the largest exporters of rails in the world -- made the alloys and carried out tests. Adaptations were made to the microstructure to allow for the manufacturing process until the final composition was perfected. Rapid industrial development by Dr Jerath, one of the company's leading research scientists, based at the Swinden Technology Centre, then transformed this concept material into an alloy which could be produced in bulk.

The new alloy has remarkable properties: it has enormous wear resistance and it also reduces wear on the wheels, which is almost unheard of. Normally, when the wear properties of the rail are improved, those of the wheels become worse.

Also, it does not become brittle, even at temperatures as low as -60°C. All this is good news as British Steel exports rails to the United States, Canada and the Scandinavian countries, where extremely cold temperatures can occur, and premium quality materials are required because of the heavy industrial railway traffic.

The alloy needs no major capital investment in new equipment because it was designed to be manufactured using existing British Steel plant.

Other applications for the alloy could include earth-moving equipment and the wheels of railway rolling stock.

Dr Bhadeshia said: "This is a story about basic science and real, enthusiastic, collaboration from industry. To take a material from the laboratory to production takes dedication and British Steel was quite happy to do all that work."

Updated: 19 June 1996