Abstract
The influence of P and S on ductility dip cracking susceptibility in thereheated weld metal of alloy 690 was evaluated by the spot Varestraint testusing different alloy 690 filler metals, while varying the contents of P andS. The ductility dip cracking susceptibility was reduced with a decrease inthe content of P and S in the filler metal; the amount of (P+1·2S)in the weld metal should be limited to 30 ppm in order to prevent microcrackingin the multipass weld metal. A numerical simulation of cosegregation behaviourof P and S revealed that both elements were segregated at the grain boundaryin the ductility dip temperature range during multipass welding. A molecularorbital analysis has suggested that ductility dip cracking can be attributedto grain boundary embrittlement due to grain boundary segregation of P andS.
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