The effect of upset conditions on the mechanical properties of flash-butt welded joints in worn high strength premium rail steel

A series of mobile flash-butt welds in a combination of new and worn high strength 68 kg/m rail were manufactured with upset distances ranging from low (11 mm) to high (18.4 mm). Tensile test pieces were prepared from a number of positions in each weld to examine the influence of both rail condition (i.e. new vs worn) and upset distance on bond strength. Additional tests were performed to determine the parent rail compositions associated with each weld, as well as the hardness distribution in the web. The results of the test program showed that in the absence of flat-spot defects, variation of the forging distance did not measurably influence the tensile strength in a consistent manner across all test positions. However, forging distance did appear to be linked with the prevalence of specific types of flat-spots, including voids and flat spots, at the bond line. The experimental results showed that it is imperative that the upset cycle is sufficient to close up voids and extrude the bulk oxides responsible for dull type flat-spots.