Formation of the Carbon-Enriched Zone and Its Evolution During the Long-Term Aging Process for 9% Cr-CrMoV Dissimilar Welded Joint

The appearance of carbon migration in the 9% Cr-CrMoV dissimilar welded joint was resulted from the sharp content transition of the strong carbide-forming element Cr between the weld (~2.3 wt%) and the base metal (~10.6 wt%). The width of the carbon-enriched zone (CEZ) under original state was about 46 μm, and the width of CEZ increased and then kept in 65 μm during the 10,000 h aging treatment. The microhardness test showed that the carbon-depleted zone (CDZ) exhibited low hardness value (~220 HV) compared with that (~340 HV) in CEZ. The significant difference in carbide content was the crucial factor in the sharp change of hardness adjacent to the fusion line. Thus, it is important to understand the evolution of the CEZ to experience a long-term aging to avoid its negative influence on the impact toughness and fatigue performance.