Stress rutpure behavior of transition joints between modified Kr-Mo steel and 316 L(N) SS

Stress rupture tests were performed on welded joints between modified 9Cr-1Mo steel and Alloy 800 as part of a trimetallic (Grade 91 - Alloy 800 - 316 L(N)) SS transition joint. For comparison, tests were also conducted on direct bimetallic (Grade 91 - 316LN) joints. The results show that the performance of the Grade 91 - Alloy 800 weldments is only a marginal improvement over the Grade 91 - 316LN joints. However, both these are considerably superior to joints involving the conventional 2.25Cr-1Mo steel as the ferritic component. Most failures occurred in the Grade 91 HAZ 1-2 mm from the weld interface. Metallographic characterization revealed features that correlated well with the softening that occurred in this region during creep testing.