New insights to damage initiation during creep deformation of stainless steel weld joints

A systematic investigation has been carried out to asses the creep cavitation behaviour in austenitic stainless steel fusion zone by performing detailed microstructural and finite element analysis. Metallographic observations of the failed cross-weld joint specimens reveal that the cavities nucleated in the near-crown region and propagated towards the near-root region. Similar pattern of nucleation and growth of cavities was observed in weld joint tested at a different stress level. The preferential nucleation of creep cavities in the near-crown region of the weld joint can be attributed to both micro and macro inhomogeneities in the weld joint. The micro-inhomogeneity in the fusion zone, which could be characterized using electron backscatter diffraction studies, is a result of variations in morphology and formation of thermo-mechanically treated region across the weld pass interface. The considerable strength variation between the heat affected zone, base metal and fusion zone resulted in macro-inhomogeneity in the weld joint and introduced significant stress gradients which could be illustrated using finite element analysis. Both micro and macro-inhomogeneities have a synergistic role in determining the damage initiation location in multi-pass stainless steel weld joints subjected to creep.