INFLUENCE OF WELD THERMAL CYCLE ON PROPERTIES OF FLASH BUTT WELDED MN-CR-MO DUAL-PHASE STEEL

Flash butt welding of 3.7 mm thick Mn-Cr-Mo dual phase steel was carri ed out at different final jaw distance (FJD), where besides normal mac hine cooling (NMC), various instantaneous post weld cooling such as fo rced air cooling (FAC) and water spray cooling (WAC) were used. The en ergy input during welding was kept practically constant. The aim of th e investigation was limited to study the influence of variation in wel d thermal cycle, resulting from the change in FJD and post weld coolin g, 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 dista nce of about 6.0 mm from the weld centre. During slow cooling, especia lly under NMC, the variation in FJD was found to reduce relatively the elongation of the weldment without affecting its UTS significantly wh ere, the weldment was generally found to fail from HAZ, 6-7 mm away fr om weld centre. However, in case of fast cooling, especially under WSC , the variation in FJD was found to have an insignificant effect on th e tensile properties of the weldment and the weldments were generally observed to be fractured from the base material.