Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds

Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulphate and fluoride at 400 oC. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FEG-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed. (author)