Creep Performance Modeling of Modified 9Cr-1Mo Steels with Oxidation

Abstract

In this study, the deformation-mechanism-based true-stress (DMTS) creep model is modified to include oxidation influence on the long-term creep performance of modified 9Cr-1Mo steels. An area-deduction method is introduced to evaluate oxide scale formation on the creep coupons, which is incorporated into the DMTS model formulated based on intragranular dislocation glide (IDG), intragranular dislocation climb (IDC), and grain boundary sliding (GBS) mechanisms, in modifying the true stress. Thus, the modified DMTS model can not only describe the creep curve, but also predict the long-term creep life and failure mode, which is shown to be in good agreement with the creep data generated in the authors’ laboratory as well as by the National Institute for Materials Science (NIMS) of Japan for long-term (> 104 hours) creep life prediction on Grade 91 steels. In particular, the predictability of the model is demonstrated in comparison with the Larson–Miller parameter method. In addition, the modified DMTS model provides quantitative information of mechanism partitioning, insinuating the failure mode via intragranular/intergranular deformation. Therefore, it has advantages over the empirical models in providing physical insights of creep failure, which can be useful to material design for performance optimization.