WITHDRAWN: Dislocation-based constitutive modeling of martensitic/ferritic steels at elevated temperatures. Part II: Cyclic behavior without hold time effects

Abstract

Grade P91, from the class of high chrome (9–12%) martensitic/ferritic steels, is one of the common candidate materials for elevated temperature structural components. Existing literature suggests that grade P91 steels exhibit signi“cant cyclic softening under low cycle fatigue (LCF) loading at temperatures between 450 �C and 600 �C. Since laboratory experiments are conducted under accelerated testing conditions, analytical modeling – with input from test data – can greatly assist in predicting the in-service response of a material. In such an effort, the current work presents a novel constitutive model – that relates the in”uence of various independent test variables such as temperature and strain-rate – for simulating the uniaxial LCF deformation behavior of grade P91 steels at 625 �C without hold time effects. The proposed minimal approach is based on the cumulative interplay physics of two types of dislocation densities that nucleate and operate at two distinct microstructural scales. The physical basis for the model is brie”y discussed for both monotonic and cyclic loading along with a detailed description of the model implementation for cyclic loading. With just two evolutionary indices each for cyclic loading and unloading, the hysteresis loops and degree of cyclic softening of grade P91 are accurately reproduced for three strain amplitudes of ±0.25%, ±0.5% and ±0.75%. Robust demonstration of predictive capabilities on the basis of the underlying physical mechanism and analytical formulation of the model is presented. In this context, the variability in deformation response until LCF failure between tests conducted under identical testing conditions is also shown to be inherently accounted using minimal experimental data (“rst 10 cycles only).