Niobium in rail steel

The present paper reviews the key developments that have taken place in the production of niobium containing rail steels. An overall perspective is given on the fundamental metallurgical principals behind such steels together with the process developments that have taken place in Europe, the USA and Japan. A number of strategies are described for the production of as-rolled high strength alloy rail steels; the options of adding further alloying elements is compared to making a eutectoid carbon rail steel whose head is hardened by reheating and accelerated cooling (slack quenching). Furthermore, the recent developments in Japan in the development of niobium containing bainitic rail steels are also discussed. Specific attention is given to the need for improved wear resistance, shelling resistance, ductility and the weldability requirements of modern track systems. The role of niobium is found to consistently provide a fine austenite grain size at the start of the head hardening treatment even with a fairly wide range in the production parameters of time and temperature. The grain refining effect results in a finer pearlite colony size by reduction of the interlamellar spacing, which in turn leads to the prevention of rail head damage through the improvement in ductility. (AU)