Hot Cracking Susceptibility of Commercial Alloy 52 Filler Metals in Multipass Welding of Alloy 690

Hot cracking behavior in alloy 690 multipass welds using commercial alloy 52 filler metals was investigated.   Six kinds of alloy 52 filler metals with different amounts of alloying elements such as Nb, Ta, Mo, Ti and Al were employed.  Cracking susceptibilities of ductility-dip and liquation/solidification cracks in the reheated alloy 52 weld metals were evaluated by the spot- and transverse-Varestraint tests.   The filler metals containing Nb, Ta and Mo were less susceptible to ductility-dip cracking, while solidification/liquation cracking susceptibilities were heightened in them.   Ductility-dip cracking susceptibility was decreased with an increase in tortuousness of grain boundary in the weld metal.   The addition of Nb, Ta and Mo to the filler metal would promote the tortuous grain boundary which resulted in the improved ductility-dip cracking susceptibility because they enhance the constitutional undercooling (the unstability of the solidification boundary) as well as the grain boundary pinning caused by the formation of carbides in weld metals.   On the other hand, the addition of Nb, Ta and Mo to the filler metal raised solidification/liquation cracking susceptibilities attributed to enlarging the solid-liquid coexistence temperature range of the weld metal.