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

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 degrees 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 triaxiality 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 mot, which seems to be induced by the combining action of equivalent stress and stress triaxiality. 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.

Automated summary

This study elucidates the effects of different stress states on creep damage mechanisms in 9-12%Cr steels under long-term high temperature exposure. Equivalent stress and stress tri-axiality have different impacts on the creep damage behavior of notched components, with the variation of stress states being evidenced by hardness distribution.