Creep damage and fracture behaviour of a type 316L(N) stainless steel and its weld metal

Creep deformation and fracture behaviour of a nitrogen bearing type 316L st ainless steel and its weld metal at 873 and 923 K are reported. At both the temperatures, the weld metal exhibited rupture lives lower by a factor of 5 to 10 than those of the base metal depending on the applied stress (sigma ) level. At 873 K, the minimum creep rate ((epsilon) over dot(s)) for the w eld metal was higher at high stresses and lower at tow stresses compared to the base metal. At 923 K, however, the weld metal exhibited epsilon (s) lo wer by a factor varying from 5 to 10 compared to that for the base metal. T he rupture ductility of the weld metal was always found to be lower than th at of the base metal for identical test conditions. Validity of Monkman-Gra nt and modified Monkman-Grant relations was examined for both base and weld metals. It was found that the base metal obeyed both the relations in the whole range of tear conditions with a single slope, while the weld metal ex hibited two slope behaviour. The observed differences are discussed in the light of transformation of delta -ferrite into brittle phases like sigma ph ase and its influence on deformation and damage.