Abstract
The T92/HR3C dissimilar metal weld joints were fabricated by manual tungsten inert gas (TIG) welding with Inconel 82 as the filler metal. After fatigue tests at 640 °C, it was found that the location of the fatigue fracture shifted from the weld metal (WM) to the heat-affected zone of the T92 steel (T92-HAZ) with a decrease in stress amplitudes (171–189 MPa to 155–166.5 MPa). The fatigue crack propagation behavior of the two fracture modes mentioned above was monitored by an in-situ scanning electron microscopy (SEM) imaging test. In addition, the results of the transmission electron microscopy (TEM) analysis showed that under high-stress amplitudes, the initiation of cracks at the weld metal was caused by the interaction between dislocations with Nb(C,N) in the matrix and M23C6 on the grain boundary. At long-term high temperature, the carbides precipitated in the weld metal played a role in strengthening the grain boundaries, so the matrix structure still maintained high strength and stability. However, the dislocation movement in the T92-HAZ accelerated the transformation of lath martensite into equiaxed subgrains, and the coarsening and aggregation of Cr-rich M23C6 carbides resulted in the initiation of cracks in this region. Therefore, as the stress amplitude decreased, the fatigue fracture location of the DMWJs shifted from the weld metal to T92-HAZ.
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