Weld metal creep-fatigue life prediction by modeling the microstructure degradation due to the exposure to high temperature and load

A new analytical method to evaluate creep-fatigue strength of stainless weld metals that were suffering from microstructure degradation was proposed. Based on the observation that creep-fatigue crack initiated adjacent to the interfaces of (sigma) and 5-ferrite, an FE-model that consisted of matrix, (sigma) and 5-ferrite was developed. The volume fraction of the (sigma) in the model corresponded to the maximum amount of precipitation expected, which means that the model represents the degraded microstructure after long-term exposure to high temperature and load. Using the model, microscopic concentration of stress and strain adjacent to the interfaces were calculated. Fatigue and creep damage were consequently evaluated which allowed creep-fatigue life evaluation. The predicted results reproduced experimental results with sufficient accuracy in a relatively higher strain region. Validation in lower strain region is expected.