Microstructural damage mechanics-based model for creep fracture of 9%Cr steel under prior fatigue loading

Abstract

Predicting the remnant creep fracture life precisely is crucial for ensuring safety of high temperature components. This study presents a microstructural damage mechanics-based model for creep fracture of 9%Cr steel under prior fatigue loading. Microstructure observation reveals that the decrease of dislocation density and the growth of martensite lath width occurred during prior fatigue process contribute to the degradation of creep strength. Particularly, coarsening of martensite lath width plays the dominated role. To take into account the effect of the prior fatigue loading, kinematic damage equations that represent the evolution of dislocation density and martensite lath are proposed in the developed model. With the proposed model, creep fracture life and creep failure strain at various lifetime factions, strain amplitudes and hold times of prior fatigue loading can be satisfactorily predicted, which manifests that the proposed model is robust in capturing the effects of various prior fatigue loadings. The proposed model is also shown to be able to accurately predict prolonged creep deformation of other similar steel after different prior fatigue loadings.

Analysis on stress‐strain behavior and life prediction of P92 steel under creep‐fatigue interaction conditions

“…Besides the loading mode, the exertion of duration period also influenced the creep‐fatigue performance. The effect of prior CFI damages and prior fatigue damage on remaining tensile and creep properties of 9%Cr steel was studied by Zhang et al 30,31 and revealed the prior performance could significantly reduce tensile strength and creep resistance. When studying the performance of alloy 709, Porter et al 32 and Amrita et al 25 also found that creep‐fatigue life was reduced in comparison with low cycle fatigue life at different temperatures, and more life reduction was observed at low temperature.…”