Railways rails - Metallurgical aspects

Rails, whose purpose is to support train axles and guide them through curves (sometimes with a tight radius of less than 200 meters), are a major safety factor for people and goods being transported.

The rails are supported by sleepers, either creosoted wood on older tracks, or concrete on modern tracks; European tracks have 1,700 sleepers per kilometer (2,000 for heavily loaded tracks). The rails rest on the sleepers, which are themselves supported by a thick layer of graded stone ballast, via rubber pads secured by elastic steel spring clips.

They are subject to wear and tear, and to internal and surface fatigue faults, which can lead to brittle fractures and derailments that are all the more serious when the accident occurs on a curve.

It is therefore an extremely noble product, requiring high-purity steel and a suitable microstructure (pearlitic to the present day).

In addition to final manufacturing checks, this product must be ultrasonically and visually inspected on the track, at a frequency appropriate to the track and the type of rail traffic.

The rail is manufactured in oxygen steel mills or electric steel mills, using continuous casting and vacuum hydrogen degassing; it is then hot-rolled in its final section on a so-called "universal" rolling mill, which rolls both the head and the base, as well as both sides of the web.

The steel rail-wheel contact requires low rolling coefficients, and wear, although measurable, remains moderate. As a result, rail or wheel changes are limited, and energy consumption remains the lowest of all means of transport; the process is therefore economically attractive, and can be extended to high-speed TGV tracks and heavier trains. The article describes the various types of rail and their conditions of use, followed by a description of the manufacturing processes.