Creep Deformation Behaviour of Modified 9Cr-1Mo Steel Clad Tubes

Abstract

Modified 9Cr-1Mo ferritic steel has been considered as the cladding tube material in Metallic Fuel Fast Reactor, in view of its inherent void swelling resistance. Creep studies were conducted on modified 9Cr-1Mo steel clad tubes at 823, 873 and 923 K at various stress levels. The resultant rupture lives ranged from 100 to 16,000 h. The creep curves exhibited a negligible loading strain, a small primary, and extensive tertiary regions at all the test conditions. A power law relationship was followed between minimum creep rate and applied stress, and the stress exponent obtained was characteristic of the precipitation hardened alloys. The stress exponent decreased with increase in temperature. Apparent activation energy for creep, in the present study, was estimated to be around 365 kJ/mol. An inverse power law relation was obtained between applied stress and rupture lives, and the corresponding stress exponent decreased with increase in temperature. The relation between deformation and fracture for these clad tubes was established using Monkman-Grant and Modified Monkman-Grant relationships. Scanning electron microscopic investigations revealed coarsening of precipitates after long term creep exposure. The creep properties generated in the current study compare well with the NIMS (Japan) clad tube data at 823 K and 873 K.