2016 Volume 34 Issue 3 Pages 181-188
Ductility-dip cracking susceptibility in the laser multipass weld metal of alloy 690 was quantitatively evaluated using different filler metals varying the contents of P and S. In order to synthesize a ductility-dip crack in the laser multipass weld metal, the cross-bead longitudinal-Varestraint test with laser welding was applied under the various welding speed. The ductility-dip temperature range (DTR) was increased with an increase in P and S contents in the weld metal, and S was more effective to enhancing the DTR compared with P. Furthermore, the DTR was decreased with an increase in the welding speed. A numerical simulation of grain boundary segregation of P and S revealed that the segregated concentrations of P and S at grain boundaries were increased with an increase in the P and S contents in the weld metal, and that those were slightly decreased with an increase in the welding speed due to the rapid heating and cooling rates. It follows that the changes in ductility-dip cracking susceptibility with the filler metal composition and welding speed were consistent with the grain boundary segregation behaviours of P and S during laser multipass welding process. According to the regression analysis of the DTR, ductility-dip cracking in the laser multipass weld metal would be inhibited by reducing the segregated concentration at grain boundary (P+2.42S) to less than approx. 8at%.
