The critical part of the transition metal joint between type 304 stainless steel and 2.25Cr-1Mo steel, with an immediate piece of Alloy 800, is the Alloy 800/2.25Cr-1Mo steel joint welded with Inconel 182. The performance of this trimetallic transition joint was studied by accelerated thermal cycling of the Alloy 800/2.25Cr-1Mo steel joint after subjecting it to its optimum post-weld heat treatment. The thermal cycling test procedure employed produces accelerated failures in transition metal joints similar to those observed in steam generators of operating power plants. The changes in the ferritic steel heat-affected zone on thermal cycling were also studied. The results of this study show that there is a marked improvement in performance, with at least a four-fold improvement in the life of the transition metal joint, on using the trimetallic configuration, instead of the direct (bimetallic) configuration.