Creep Life Prediction of Modified 9Cr-1Mo Steel under Multiaxial State of Stress

Creep life prediction of modified 9Cr-1Mo steel under multiaxial state of stress has been carried out in the present investigation. Creep tests were carried out on smooth and notched specimens of modified 9Cr-1Mo steel in the stress range 150 - 230 MPa at 873 K. The creep rupture life was found to be higher in the presence of notch than that of smooth specimens indicating ‘notch strengthening’ behaviour. The extent of strengthening tends to saturate for relatively sharper notches. Finite element analysis was used to estimate the variation of stresses across the notch throat plane. As the stresses varied across the notch throat plane, the stresses at the skeletal point were used for estimating the representative stress. The models proposed by Cane, Hayhurst and Nix were examined for creep life prediction under multiaxial state of stress. The von-Mises stress was found to predominantly govern the creep rupture life of the steel. The creep rupture life has been predicted based on Cane's model using finite element analysis and continuum damage mechanics.