Austempered ductile iron (ADI) for railroad wheels : final report.

PDFTech Reporthttp://www.nurailcenter.org/research/final_reports/MTU/NURail2012_MTU-R01-Final_Report_Submitted.pdfNURail2012-MTU-R01DTRT12-G-UTC18RailroadsIronWheelsets (Railroads)Railcar structural componentsDecompositionPerformance testsThermodynamicsMichiganNational University Rail Center (NURail)Warsinski, KarlSanders, Paul G.Michigan Technological University. Department of Materials Science and EngineeringUniversity of Illinois at Urbana-ChampaignNational University Rail Center (NURail)United States. Dept. of Transportation. Office of the Assistant Secretary for Research and TechnologyUnited States. Dept. of Transportation. University Research ProgramLautala, Pasi TapioUS Transportation CollectionThe purpose of this project is to investigate the potential for austempered ductile iron (ADI) to be used as an alternative material for the production of rail wheels, which are currently cast or forged steel which is commonly heat treated. ADI has several potential advantages over steel, including lower production costs (20% savings for a typical component) while maintaining strength-to-weight ratios equivalent to heat treated steels, and microstructure-based noise damping[1]. Preliminary work in Europe also suggests that ADI wheels may reduce both wheel and rail wear, increasing equipment and infrastructure life [2]. There are concerns about the fatigue cracking of ADI wheels due to localized strain-induced transformation of austenite to martensite. However, appropriate wheel design adjustments can be made to address this [3]. In order to take advantage of these characteristics, it is necessary to first characterize ADI\ue2\u20ac\u2122s microstructural stability with respect to elevated temperatures that result from on-tread braking. The key microstructural component in ADI is ausferrite, which is a combination of the stable room temperature phase (ferrite) with the meta-stable higher temperature phase (austenite). Because of the presence of the meta-stable austenite phase, ADI is susceptible to changes in properties at elevated temperatures. Heat-treated steel wheels currently in use are also susceptible to changes in structure and properties as a result of overheating. The primary purpose of this project is to identify the conditions necessary for the decomposition of the ausferrite microstructure and compare them with rail wheel service conditions. Then, methods for stabilizing the ausferrite structure thermodynamically and kinetically are explored. It should also be noted that the minimum mechanical properties of the standard ADI grades do not align well with the AAR standards for rail wheel properties. Standard ADI is permitted to have lower elongation in all grades than is permitted for rail wheels [4], [5]. Grades 3-5 meet the strength requirements for rail wheels, but as the strength increases the minimum elongation falls farther from the value required by the AAR standard