Many members of the department over the years have shown a fascination with bainite and with phase transformations in general. The painstaking studies conducted in this area are now bearing fruit, as demonstrated by some recent collaborative work with British Steel. As a result of a colloquium presented at the Swinden Laboratories on the subject of "Bainite", the Department was challenged to come up with a design for rail steels. Conventional rail steels are basically pearlitic and rely on the presence of hard cementite for wear resistance. However, cementite is also rather brittle so that such rail steels lack toughness. Toughness is a useful property for rail steels, not only for resistance to gross fracture, but also in influencing the wear behaviour.
Using the theory developed for phase transformations in steels, it was possible in a very short time to computer-design three alloys without doing any experimental work. The alloys were configured to have a radically different carbide-free bainitic microstructure.
They were made and tested at British Steel, and found to exhibit exceptionally good wear and toughness properties. Experimental measurements confirmed the alloy design procedure and industrial scientists rapidly translated the concepts into a steel which could be produced in bulk and in available processing plant. These new types of rail steels represent a sizeable export market for British Steel; the track is currently undergoing trials in Switzerland, USA and Germany and preparations are being made for full-scale marketing.
The steels produced are basically low carbon, carbide-free, bainitic steels. The hardness is achieved by the fine grain size, rather than with cementite. The steels, which contain common alloying additions, are cheap to produce; it is only the microstructure which is different in the context of rails. Moreover the hardness is uniform throughout the rail cross-section.
Computer modelling as a means of designing new steels is now a very powerful tool. British Steel certainly have great confidence in this work, and currently are sponsoring several projects in this area in the Department.
Enquiries to : Dr Harry Bhadeshia (01223) 334301
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