Abstract
The mechanism for creep rupture of 12%Cr /alloy 4715 welded joints was investigated by employing traditional uniaxial tensile creep in this study. The creep tests were maintained at 580 °C with creep loading stresses gradually decreasing from 300 to 240 MPa, and the time to failure was tested. The rupture location shifts from base metal (BM) to BM + fusion line (FL) then to FL + fine grain zone + coarse grain zone (CGZ), and finally to FL + CGZ as holding time increases. Meanwhile, a softening phenomenon is also observed in the heat-affected zone (HAZ) in crept specimens for a more extended holding time, where voids, carbides, and dislocation density are further discussed. The carbides are identified as Cr and Mo-rich M23C6 type, which forms mainly at grain boundaries during creep testing. In HAZ, M23C6 gradually increases and coarsens, providing nucleation sites for creep voids. Finally, the Larson–Miller parameter method is employed to provide a theoretical reference for predicting use cases that satisfy the industry service condition.
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