Rail Steels: Part One

Modern railway systems are subjected to intense use, with fast trains and increasing axle loads. Rails have to be more wear resistant and achieve higher standards of straightness and flatness in order to avoid the surface and internal defects which may lead eventually to failure. The shape of the manufactured rail depends to a large extent on the uniformity of thermo mechanical processing; the most advanced mills are computer controlled with continuous feed-back from the product during manufacture.

Up until the 1970s, railway rails for passenger and freight trains were regarded as relatively simple undemanding products and the specifications had changed very little for decades. However, investments in railway systems, the advent of high-speed passenger trains and the requirement for longer life track imposed a demand for high quality rails, greater strength and tighter geometric tolerances. Therefore there have been major innovations in the past 20 years in terms of the method of manufacture, degree of inspection and range of products.

Rail steel is extremely tough. As figure 2, rail steel resists breakage even after the yield point is exceeded. In addition, rail steel has satisfactory amount of ductility and after re-heating, can be used to complete most forming operations.

Their average yield point is greater than 60,000 PSI, while actual tensile strength normally ranges from 100,000 PSI to 130,000 PSI. This high yield point means rail steel provides ample stiffness, enduring heaviest demands with little deformation.

Even after years of service and high stress, there is no difference between the grain structure of a used rail and a new rail. Age, traffic and weather do not change its basic properties. All stresses are relieved through heating prior to being re-rolled. This re-rolling, in accordance with ASTM-A-499, decreases the rails’ grain size, and that means improved resiliency. The additional working of the steel actually makes it better than when it was a rail!