Creep Rupture Properties of an Austenitic Steel with High Ductility under Multi-axial Stresses

Abstract

Using tubular specimens of austenitic steel SUS310S with high ductility, creep rupture tests are conducted in tension, torsion and combined tension-torsion stress states at 700°C. It is found that the maximum principal stress determines the multi-axial creep rupture life of the steel. The reasons are assumed to be that many voids nucleated in the early stages of creep, and that at any creep stress states this steel showed larger deformations and continuous nucleating of voids during creep testing. Furthermore, by observing on the scanning electron micrographs, the specimens ruptured at various stresses are found to exhibit different fracture modes. These creep fracture modes and their formatting factors are discussed in detail. It is assumed that at a multi-axial stress state, the von Mises equivalent stress promotes creep deformation and nucleation of creep voids, meanwhile the growth of the voids should be restrained by the large creep deformation. It is further suggested that in a specimen with existing of the mean stress and a smaller equivalent stress, a brittle intergranular fracture should occur easily.