Abstract
This work concerns a study into the design of creep resistant precipitation hardened austenitic steels for fossil fuel power plants using an integrated thermodynamics based model in combination with a genetic algorithm optimization routine. The key optimization parameter is the secondary stage creep strain at the intended service temperature and time, taking into account the coarsening rate of MX carbonitrides and its effect on the threshold stress for secondary creep. The creep stress to reach a maximal allowed creep strain (taken as 1%) at a given combination of service temperature and time is formulated and maximized. The model was found to predict the behavior of commercial austenitic creep resistant steels rather accurately. Using the alloy optimization scheme three new steel compositions are presented yielding optimal creep strength for various intended service times up to 105 hours. According to the evaluation parameter employed, the newly defined compositions will outperform existing precipitate strengthened austenitic creep resistant steels.
