Creep deformation behaviour of alloy D9 cladding tubes

Creep properties of Alloy D9 (a titanium- modified austenitic stainless ste el) cladding tubes in 20% cold worked condition have been evaluated at 973 I; in die stress range 125-250 MPa and compared with creep properties of 20 % cold worked 316 stainless steel cladding tubes and 20% cold worked Alloy D9 bars produced indigenously. Alloy D9 cladding tubes exhibited a lower cr eep rate and a prolonged secondary stage compared to 316 stainless steel cl adding tubes. The creep deformation behaviour of both Alloy D9 and 316 stai nless steel cladding tubes could be described by a power law relationship b etween steady state creep rate and stress. Steady state creep rate of Alloy D9 was lower by an order of magnitude as compared with 316 stainless steel cladding tubes. Rupture lives of Alloy D9 cladding tubes were found to be nearly six times higher than the rupture lives of 316 stainless steel cladd ing tubes. The rupture ductility of Alloy D9 cladding tubes was less when c ompared with 316stainless steel cladding tubes. Alloy D9 cladding tubes exh ibited higher rupture lives than the bars under identical stress conditions . Metallographic investigations carried out on Alloy D9 bars revealed exten sive creep damage in the form of wedge- type cracks. The creep properties o f Alloy D9 have been rationalised on the basis of precipitation and damage behaviour.