Microstructure evolution and its effect on the stress rupture behavior of 9%Cr-CrMoV dissimilar welded joint

Taking the economic factor into account, 9 %Cr martensite heat-resistant steel is chosen to be joined with CrMoV steel by welding technique to utilize their potential at different temperatures. In the present study, the dependence of rupture time on the applied stress was determined and in accordance with the equation of lg(tr) = 7.224-0.014 sigma. All the stress rupture specimens were ruptured in the base metal of CrMoV steel (CrMoV-BM), indicating the high welding quality and the slight effect carbon migration on the stress rupture properties. The microstructure charac-terization revealed that the M23C6, M7C3 and MX type carbides were identified in the CrMoV-BM in the original state. These carbides were the typical precipitates existed in the heat resistant steel. Partially coarsened carbides and Mo-rich M6C phase were detected during the stress rupture test. The micro-voids tended to be initiated in the regions near these partially coarsened carbides and Mo-rich M6C ones along the grain boundaries. Subsequently, the macro-cracks formed via the micro-void convergence and eventually caused the fracture of the ruptured specimens.