Exploration of the competing failure during the stress rupture process for 9Cr-CrMoV dissimilar welded joint

The competing failure mechanism between the heat affected zone (HAZ) of CrMoV steel and weld metal (WM) was found by the stress rupture tests for the 9Cr-CrMoV dissimilar welded joints. The stress rupture occurred in the HAZ of CrMoV steel for the welded joint by the 9Cr steel without element W, yet the failure location shifted to the WM for the welded joint by the 9Cr steel with element W. The precipitates in the WM were mainly the Cr- and Mo-rich M23C6 type carbides. While the W-rich particles were detected in the region of the WM near the fusion line. The partially melted BM2 and its movement into the WM during welding could trigger the formation of the W-rich particles. Thus, the formation of the harder and more brittle W-rich particles in the WM near the fusion line is considered as the crucial factor to result in the failure transition.