Residual stresses in thermite welded rails: significance of additional forging
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RESEARCH PAPER
Residual stresses in thermite welded rails: significance of additional forging B. Lennart Josefson 1
&
R. Bisschop 1 & M. Messaadi 2 & J. Hantusch 3
Received: 6 December 2019 / Accepted: 27 April 2020 # The Author(s) 2020
Abstract The aluminothermic welding (ATW) process is the most commonly used welding process for welding rails (track) in the field. The large amount of weld metal added in the ATW process may result in a wide uneven surface zone on the rail head, which may, in rare cases, lead to irregularities in wear and plastic deformation due to high dynamic wheel-rail forces as wheels pass. The present paper studies the introduction of additional forging to the ATW process, intended to reduce the width of the zone affected by the heat input, while not creating a more detrimental residual stress field. Simulations using a novel thermo-mechanical FE model of the ATW process show that addition of a forging pressure leads to a somewhat smaller width of the zone affected by heat. This is also found in a metallurgical examination, showing that this zone (weld metal and heat-affected zone) is fully pearlitic. Only marginal differences are found in the residual stress field when additional forging is applied. In both cases, large tensile residual stresses are found in the rail web at the weld. Additional forging may increase the risk of hot cracking due to an increase in plastic strains within the welded area. Keywords Aluminothermic welding . FEM . Residual stress . Hardness . Pearlite
1 Introduction Continuous welded rails have been in use since the 1930s. The most common continuous welding method for welded rails, or welded segments of rails, in the track is aluminothermic welding (ATW), see for example Meric et al. [1] and Chen et al. [2]. This method is also considered for replacing defective or broken rails (or welds) and installing rail insulation joints. In ATW, the rails are properly cut, cleaned, and aligned. The two rail sections are then positioned collinearly with a gap in between before a ceramic mold is placed around them. The two rail ends are then preheated with an oxy-propane torch. Recommended for publication by Commission X - Structural Performances of Welded Joints - Fracture Avoidance * B. Lennart Josefson [email protected] 1
Department of Industrial and Materials Science, Chalmers University of Technology, Göteborg, Sweden
2
Faculty of Civil Engineering and Geosciences, Railway Engineering Group, Delft University of Technology, Delft, The Netherlands
3
Goldschmidt GmbH, Leipzig, Germany
This ensures that the assembly is dry. In the next step, a reaction crucible is mounted on the top of the mold. The crucible is filled with thermite, consisting of iron alloy, iron oxide, and aluminum granules. Upon ignition, a highly exothermic reaction melts the mixture, causing it to flow out of the crucible and into the weld gap. The molten iron provides the heat for fusion along with weld metal. After the weld pool has cooled for some time, a hydraulic shearing device removes exces
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