Thermal Cycle and Microstructure of Heat Affected Zone (HAZ) of Flash Butt Welded Mn-Cr-Mo Dual Phase Steel

Abstract

Flash butt welding of 3.7 mm thick Mn-Cr-Mo dual phase steel is carried out at different final jaw distances, where various post weld cooling systems such as the normal machine cooling, forced air cooling and water spray cooling are used. The energy input during welding such as the current and voltage are kept constant. The intention of this investigation is limited to study the influence of various weld thermal cycle on the behaviour of phase transformation at weld centre and different regions of HAZ. Under different conditions of welding the weld thermal cycle is analysed and the behaviour of phase transformation at different regions of the weldment is determined with the help of welding CCT diagram. A detail microstructural study is carried out under optical and scanning electron microscopes. A special attention is paid to study the behaviour of tempered martensite region of HAZ, which is identified earlier as the weakest region of HAZ, under different welding conditions. The weakening of tempered martensite region is estimated by measuring its microhardness under different conditions of welding. © 1990, The Iron and Steel Institute of Japan. All rights reserved.