Abstract
Flash butt welding of 3.7 mm thick Mn-Cr-Mo dual phase steel was carried out at different final jaw distance (FJD), where besides normal machine cooling (NMC), various instantaneous post weld cooling such as forced air cooling (FAC) and water spray cooling (WAC) were used. The energy input during welding was kept practically constant. The aim of the investigation was limited to study the influence of variation in weld thermal cycle, resulting from the change in FJD and post weld cooling, on the properties of the weldment. It was observed that during NMC the variation in FJD influences the weld thermal cycle and properties, but the application of forced cooling reduces the influence of FJD on them. The increase of cooling rate was found to reduce the softening of HAZ, in presence of reduction in tempering of martensite at a distance of about 6.0 mm from the weld centre. During slow cooling, especially under NMC, the variation in FJD was found to reduce relatively the elongation of the weldment without affecting its UTS significantly where, the weldment was generally found to fail from HAZ, 6-7 mm away from weld centre. However, in case of fast cooling, especially under WSC, the variation in FJD was found to have an insignificant effect on the tensile properties of the weldment and the weldments were generally observed to be fractured from the base material.
