| Brief Description of Research Project |
The purpose of this project is to enable the use of Austempered Ductile Iron (ADI) in railroad wheels. It is hypothesized that ADI wheels might provide considerable benefits to the railroad industry, as ADI railroad wheels have the potential to be 10% lighter than steel wheels with greater damping, higher wear resistance, and lower cost. Both cast steel and ductile iron rail wheels are heat treated, but ADI has 20% lower cost due to better castability, reduced melting temperature (due to the higher carbon level), and lower heat treating cost. In addition to reduced maintenance due to wear resistance, ADI wheels could provide increased loading capacity for freight railroads without any changes in car design. For higher speed passenger equipment, they might provide better train performance due to lighter structures. However, thermal cycles due to braking may cause thermal degradation of the ADI microstructure leading to premature failure. This project will first characterize the temperature profile of rail wheels in service, and then characterize thermal stability of existing ADI grades. Based on literature data, chemical composition and production parameters of ADI will be optimized to stabilize the ausferrite microstructure during exposure to rail wheel thermal cycling. This project will cover the development of ADI specifications that will allow ADI wheels to enter qualification trials in accordance with AAR standards. Evaluation of existing grades of ADI will be completed first, followed by alloy and heat treatment adjustments as necessary. The project will not progress to full qualification of the material, as individual wheel producers do that testing. Characterization will include differential thermal analysis to determine the start temperature for microstructure degradation. Further, material properties will be tested at various times and temperatures to determine when mechanical properties of ADI wheels fail to meet standard requirements. New alloys will be modeled thermodynamically, cast in the Michigan Tech foundry, characterized microstructurally, and tested in tension. |