Nonhomogeneous microstructure related creep damage of the CrMoV multi-pass weld metal

The metallurgical notch effect of weldment is critical for the structural integrity assessment and to avoid the premature failure especially at elevated temperature. The local nonhomogeneous microstructure located in heat affected zone (HAZ) and multi-pass weld metal area (WM) is one of the largest contributions for the material weakening of the entire weldment. Although the type IV failure related to the HAZ has been intensively discussed, few researchers focus on the creep damage on the weld metal. In fact, the limited long-term creep tests of welded joints conducted by Tabuchi et al. [4]. has emphasized the necessity of monitoring creep damage not only in the HAZ but also in the weld metal. In this article, the nonhomogeneous microstructure related creep damage of the CrMoV multi-pass weld metal is discussed in detail. Different fracture morphology subjected to different weld properties are compared with each other, including the distribution of creep cavities, the precipitates and the substructures of crept specimens sampled from weld pass metal in the welding direction (WP), the overlap of different weld passes (WPO) and multiple weld passes through the thickness direction (MWP). Further, the microscopic analysis on the heterogeneous creep damage behavior are conducted. It is found that the grain length difference perpendicular to the loading direction is the dominant reason for anisotropic creep damage of multi-pass weld metal. In addition, the mismatched creep properties of subzones in the multi-pass weld metal also affect the damage field distribution.