Role of inclusions in flux aided backing submerged arc welding

Abstract

The formation of inclusions and their roles in Ce microalloyed weld metal by flux aided backing submerged arc welding (FAB-SAW) were studied by combining experimental investigation and thermodynamic calculation. The results showed that in Ce microalloyed weld metal, the core of effective inclusions was composed of Ce2O3, Al2O3, SiO2, MnO, and TiO compound oxides, while the surface of inclusions was composed of CeS. The first-formed Ce2O3 particles in molten pool provided more nucleation sites for Al, Si, Mn, Ti oxides and CeS, which promoted an increase on the areal density and a decrease on the mean diameter of inclusions. The small sized inclusions increased the formation of acicular ferrite (AF) and suppressed the formation of grain boundary ferrite (GBF) and ferrite side-plate (FSP). The elongation, tensile strength and impact toughness of weld metals were improved with the increasing amount of AF. When 3.0wt.% CeO2 was added, the highest proportion of AF was obtained, producing the optimal mechanical properties of weld metal with elongation of 24%, tensile strength of 635MPa and impact energy of 89J at −20°C.