Stress state dependent creep damage behavior of 9–12% Cr steel notched components

Abstract

Creep damage is governed by different microstructural features (e.g. precipitate coarsening, substructure growth, cavity/crack nucleation and growth) during long term high temperature exposure in 9–12%Cr steels. The dependences of stress states (e.g. equivalent stress and stress tri-axiality) on these damage mechanisms are clarified in this work. Various stress states are produced in FB2 steel notched components with different root radii for creep tests at 605 °C. Results indicate that equivalent stress and stress tri-axiality present different influences on creep damage behavior of notched components at elevated temperatures. The equivalent stress and stress tri-axiality both enhance the precipitation of the carbide, indicating larger mean diameter and higher area of the precipitates. Meanwhile, the equivalent stress plays a more significant role on the coarsening of the substructure of the material than the stress tri-axiality. Creep cavities are mainly found at several hundred micrometers away from the notch root, which seems to be induced by the combining action of equivalent stress and stress tri-axiality. These microstructural degradation can be proved by the distribution of the hardness in the notch region of component accompanied by the variation of stress states.