Abstract
Modified 9Cr-1Mo steel is used in the high temperature environment such as water supplying pipes in steam power plant because of its low thermal activation to maintain steady rate deformation during long-term creep. In reality, however, in a long term region of, say, 100,000 h or longer, creep rupture lives become much shorter than predicted because of the material degradation which may occur due to constraint among anisotropic crystal grains around a welded joint. This paper describes a polycrystal elasto-viscoplastic finite element code considering the damage mechanics which the present authors have developed in order to analyze long-term creep behavior of a welded joint in modified 9Cr-1Mo steel at 823K in air. The results of the analyses done by the present FE code showed that creep damage preferentially occurred in fine HAZ, which implies internal crack initiation known as Type IV cracking. The developed code reproduced abrupt decrease in the creep rupture lives at lower applied stress levels.
