As transportation costs rise, rail stock material improvements are critical to improving efficiency, durability, and performance. Steel wheels have been a consistent part of rail equipment, but it may be time to assess potential other alloys and materials in anticipation of future demands. Strength requirements are steadily increasing with rail car capacity, while weight savings in equipment can reduce fuel costs and/or increase carrying capacity. Herein, the current requirements for railroad wheels are discussed and compared with experimental evaluation of a potential alternative material, austempered ductile iron (ADI).
ADI is an attractive wheel material because of its higher strength-to-weight ratio (as compared to steel) and its wear resistance. ADI castings are also typically cheaper to produce than steel. While ADI can meet or exceed the strength of steel components, it is also comparable in ductility and impact strength, so conversion to ADI does not bring additional risk of brittle fracture, as is commonly the case when achieving higher strengths.
There are challenges with its implementation, however. AAR certification of new materials is costly and time consuming, so adoption is unlikely until there is a very compelling business case. Heat produced during on-tread braking has the potential to damage the heat-treated structure of ADI. The regular exchange of cars across different sections of track and therefore different managing companies requires that new wheel materials be fully backwards compatible, so alterations in design are severely limited. This paper will take initial steps toward assessing the potential of ADI railroad wheels by investigating the performance of ADI at elevated temperatures, and comparing the results to measured and simulated wheel temperatures.