The occurrence and behavior of a carbon denuded soft zone in Cr-Mo weldments was studied to determine its influence on mechanical properties and in-service behavior. Room temperature tensile tests, creep rupture tests and Moire interferometry evaluations were performed in order to characterize the behavior of this unique zone in Cr-Mo weldments. The zone is brought about by chromium level differentials between the weld metal and base metal. Extensive metallography was accomplished using OLM, SEM and STEM techniques.Our results show that the occurrence of the carbon denuded soft zone is due to carbon migration, which is driven by elemental differences (especially in chromium) between the weld metal and base metal. The extent of carbon migration depends on the PWHT schedule. OLM characterizations show that in 2 ¼ Cr - 1Mo weld metal and 2 ¼ Cr - 1Mo base metal weldments the soft zone is widest for the A and T condition. Next widest is the N and T condition where it is only a few grains wide, while the soft zone is very narrow (a grain wider) for the PWHT condition. In a 9 Cr - 1Mo weld metal and a 2 ¼ Cr - 1Mo base metal weldment the soft zone development begins a short time after PWHT (less than 1 hr at 1350°F) in the overlapped region of the heat-affected zone (HAZ), and then spreads along the entire fusion line as time at temperature increase.