Flash-butt welding is used in the manufacture of continuously-welded rails. Finished welds typically exhibit high levels of tensile residual stresses in the rail web and at the upper surface of the rail foot, which may increase the risk of fatigue failure under in-service loading conditions. Reducing the magnitude of the residual stresses, for example by modification of the welding conditions or application of post-weld heat-treatment, may alleviate this risk. An understanding of the influence of the welding process, including the post-weld cooling conditions, short term post weld heat treatment and accelerated cooling, on the residual stress distribution is necessary in order to improve the performance of flash-butt welds through the application of post-weld heat treatment. In addition, incorrect post-weld treatment conditions that may have adverse effects on both the residual stress distribution and material characteristics in the welds would need to be avoided. A finite element model has been developed to estimate the effects of various post-weld cooling conditions on the residual stress distribution in flashbutt-welded AS60 kg/m rail. The thermal history for normal (air) cooling, rapid post-weld heat treatment, and accelerated cooling (using water spray) was computed, and used as load inputs to calculate the sequentially-coupled stress-time history which included the phase transformation characteristics of the rail steel. The predicted residual stress distributions resulting from specific heat treatment conditions were compared. In addition, the localised the influence of the initiation time for the rapid post weld heat treatment, initiation times after final upset, were on the extent to which tensile residual stresses were reduced was investigated on the reduction of tensile residual stress levels. Heating of the rail foot immediately after final upset was found to reduce the magnitude of tensile residual stresses in the web region of the weld. Preliminary numerical predictions showed that water quenching the entire weld region, too soon after the austenite-to-pearlite transformation is completed, can induce further tensile residual stresses without affecting the microstructure. The results of the numerical analysis can be used to develop modifications to the flashbutt welding procedure that should result in lower residual stress levels, and hence improved weld performance.
|Publication status||Published - 1 Jan 2007|
|Event||16th International Federation for Heat Treatment and Surface Engineering Congress - Brisbane, Australia|
Duration: 30 Oct 2007 → 2 Nov 2007
|Conference||16th International Federation for Heat Treatment and Surface Engineering Congress|
|Period||30/10/07 → 2/11/07|