INVESTIGATION ON THERMAL CYCLE AND MECHANICAL PROPERTIES OF FLASH BUTT WELDED DUAL PHASE STEEL

Abstract

Weldability of dual phase steel, a unique class of HSLA steel have gathered a wide spread attention of automobile industries for making wheels etc., under flash butt welding process is investigated. The influence of some welding parameters such as final jaw distance as well as the post weld cooling, primarily affecting the weld thermal cycle, on the microstructure of weld centre and different regions of HAZ have been studied. The effect of various weld thermal cycle on the microhardness behaviour across the weld has been analysed. The mechanical properties of the weldments, such as the ultimate tensile strength, elongation and yield strength/ultimate tensile strength ratio, prepared under different conditions of welding are studied. It has been observed that the weldment in general shows a tendency to fracture from tempered martensite region of HAZ, observed at a distance of about 6mm from weld centre, when it is prepared under normal machine cooling condition of flash butt welding process. However the use of faster cooling has been found to strengthen the tempered martensite region and especially in case of very fast cooling obtained by using water spray the weldment has been found to fail from the base metal under tensile loading. This is the primary achievement of this work which may eliminate the inherited problem of the flash butt welding of dual phase steel.