Structure and Properties of Thermite Welds in Premium Rails

PDFTech ReportDOT/FRA/ORD-85/02DOT-TSC-FRA-84-4RR519/R5304Rail (Railroads)RailroadsWeldingAlloy steelResidual stressRail steelMetallurgyThermit weldingUnited StatesUnited States. Federal Railroad AdministrationSchroeder, L. C.Poirier, D. R.University of ArizonaJohn A. Volpe National Transportation Systems Center (U.S.)United States. Federal Railroad Administration. Office of Research and DevelopmentAGR-INFRASTRUCTURE-RailroadsNTL-RAIL TRANSPORTATION-RAIL TRANSPORTATIONVolpe National Transportation Systems Center, Technical Reference CenterThermite welds were used to join combinations of premium rails and AREA Controlled Cooled Carbon rails (i.e., standard rails). The premium rails comprised head-hardened rails and CrMo, CrV and Cr alloy rails. A major objective was to determine the feasibility of joining premium rails to each other and to standard rails with the thermite welding process. The objective was met in that metallurgically sound welds were produced using either "standard" or "alloy" thermite charges. Other objectives were to determine mechanical properties and metallurgical structures of the weld-metal and of the heat-affected zones. The "alloy" weld-metal was stronger than "standard" weld metal but had less tensile ductility. Both types exhibit ductilities of only 2-6 percent reduction in area and impact energies of only 1.5-2.8 Joules at 20 deg C. Tensile and impact specimens, which straddled the region of minimum hardness at the outer edge of the heat affected zone, show tensile ductilities of 19-60 percent reduction in area and only 2.6-6.9 Joules for impact energy. In addition, temperature in the rail near the weld metal was measured as four of the welds were produced; in a fifth, temperatures in the weld metal, itself, were measured. Finally, residual stresses were determined, and their effect on fatigue strength of welded rail is discussed