Effect of multiaxial stresses on creep damage of 316 stainless steel weldments

The difference in creep strength between a base metal and a weld metal always produces a multiaxial stress state even if the macroscopic loading is uniaxial. In this study, weldments were formed between wrought 316 stainless steel and two types of 316 weld metals with slightly different creep properties and chemical compositions. Full-size 316 weldments, including base metal, heat-affected zone (HAZ) and welds, were creep tested at 650 °C. The multiaxial stress distributions in full-size 316 weldments were simulated by the finite element method (FEM). Three stress parameters, namely, the maximum principal stress (MPS), the yon Mises effective stress (VMS), and the principal facet stress (PFS), were used to correlate the local multiaxial stresses with local creep damage distributions and failure lifetime. Metallographic examination and creep rupture data showed that the PFS parameter gave the best prediction of the creep damage distribution caused by the multiaxial stresses in 316 weldments. This approach may have application in the design, life prediction, and in-service evaluation of weldments.