Creep Property Evaluation for Stress Mitigation Simulation in Post Weld Heat Treatment

Creep properties for stress mitigation simulation in post weld heat treatment (PWHT) were studied. Materials tested in this study were both deposited metal and base metal of a nickel base alloy, an austenitic stainless steel, and a low alloy steel. First, creep tests were conducted at 625 °C, which is a holding temperature in PWHT of a low alloy steel. Test specimens were subjected to certain stress and the amount of creep strain was measured. A Norton-Bailey law model was used to simulate the amount of creep strain. Material parameters for the Norton-Bailey law model were determined from the creep strain measurement data. Stress relaxation tests were also conducted at 625 °C. Test specimens were subjected to a constant total strain and stress relaxation was measured. The experimentally measured stress relaxation data were calculated using the Norton-Bailey law model with the material parameters determined from the creep tests. The calculation data showed good agreement with the experiment data. Accordingly, the material parameters determined in this study can be considered valid.