New rail steels for the 21st Century

摘要

Rail is the most valuable asset owned by railroads. In North America alone, railroads spend more than $2 billion a year on rail repair and replacement. Transportation Technology Center, Inc., in Pueblo, Colo., continuously conducts rail performance tests of the most modern premium rails developed by manufacturers worldwide. These tests are conducted to assess rail performance and compare improvements, as well as differences, among the tested rails, allowing clear identification of the improvements in the newly-developed rails. Historically, improvements in rail performance were made through the addition of alloying elements, mainly carbon. For instance, rail steels during the 1960s had approximately 0.7 wt%C that was increased to 1 wt%C in the past four decades. Figure 1 sketches the above mentioned historical pathways in the carbon content additions and provides an example of the typical microstructures for rail from different generations. In addition to the benefits of increasing carbon, a head hardening process was successfully implemented during the 1990s. Both developments have resulted in outstanding improvements in rail performance with a corresponding increase in hardness from 248 HB to more than 400 HB (rails manufactured in 2001). Although current rails have excellent wear resistance, fatigue-resistant improvements are required since a great portion of the rail is removed prematurely due to fatigue related issues.