Microstructural and Finite Element Analysis of Creep Failure in Dissimilar Weldment Between 9cr and 2.25cr Heat-Resistant Steels

Microstructural analysis and the creep failure mechanism of dissimilar weldment between ASTM A213 T92 (9Cr1.5W0.5MoVNbTi) and T22 (2.25Cr1Mo) heat-resistant steels are reported. The low-Cr part that has high carbon activity shows a depletion of C during postweld heat treatment. In particular, the soft carbon-depleted zone (CDZ) with the lowest hardness is surrounded by strong weld metal (WM) and the T22 heat-affected zone (HAZ). Load-displacement curves obtained by nanoindentation experiments are used to extract true stress–strain curves of the WM, the CDZ, and the T22 HAZ by using finite element methods (FEMs). Because of the mechanical properties of each region, the soft CDZ confined between harder regions is exposed to multiaxial stress. Therefore, creep voids actively form and coalesce in this CDZ and lead to macroscopic brittle fracture.