Effect of Enhanced Convection on the Macro-Micro-Structure of Dissimilar Ferrous Welds

For better understanding the weldability of dissimilar metals, it is imperative to examine the convective forces in the weld pool, and their effects on the macro-and microstructure of dissimilar welds. The objective of this investigation is to examine the effect of enhanced buoyancy-induced convection (> g=9.81 m/s2) on the weld pool and the solidified weld zone (WZ). The CW-GTA and the GMA welds are done at simulated 4g and 8g conditions using the MultiGravity Research Welding System (MGRWS). For CW-GTA and GMA welds, the solidification cooling rate in the WZ increases as the g-level increases. At all g-levels, the cooling rate in CW-GTA WZ is higher than the GMA WZ. The average width of the heat-affected zone (HAZ) in GTA and GMA welds decreases as the g-level increases. At all glevels, the GTA and GMA welds contain the fusion boundary transition zone (FBTZ), which includes the unmixed zone (UMZ) and the hard zone (HZ). The hardness of the FBTZ is around 425 and 325 HV in CW-GTA and GMA welds, respectively. The maximum thickness of the FBTZ in the GTA and GMA welds decreases exponentially with an increase in g-level. The microstructure of the FBTZ contains martensite.