Effect of Stress and Temperature on Rupture Life of Dissimilar Weld Joint of Austenitic 316LN SS and Ferritic-Martensitic P91 Steel

Dissimilar weld joint of P91 steel-316LN SS is widely used in power plants and is mainly subjected to creep. Creep studies for such dissimilar weld joint were carried out at two test temperatures i.e. 550 °C and 600 °C. The samples were tested under the stress levels ranging from 80 to 220 MPa. Creep life increased with decrease in applied stress at both the test temperatures. The creep life obtained at two temperatures for a particular stress level showed a drastic difference of ~ 90%. Welded creep specimens fractured at the base metal of P91 steel during creep exposure at high stress level. Fractographs of the failed specimens at P91 steel base metal showed ductile dimples and the effects of temperature and applied stress were clearly observed. Hardness profile for creep-exposed specimens was obtained across the weld regions and was compared to that of welds with post weld heat treatment (PWHT) condition. Creep exposure led to decrease in hardness values across the P91 steel HAZ, while an increase along 316LN SS and weld metal of the dissimilar weld joint.