Effect of Prior Cold Work on Creep Rupture and Tensile Properties of 14Cr-15Ni-Ti Stainless Steel

Titanium bearing 14Cr-15Ni stainless steel is the material chosen for the fabrication of the fuel clad tubes used in the Prototype Fast Breeder Reactor which is under construction at Kalpakkam. The superior swelling resistance and creep strength of this alloy is due to the intragranular precipitation of fine titanium carbides especially on dislocations. Cold work on these austenitic steels can improve both the creep strength and swelling resistance. A prior cold work (PCW) level of 20±4% is hence prescribed for materials used in the core of Fast breeder reactors (FBRs). Variation of tensile and creep properties within this cold work range is required to be evaluated, to check if the range of cold work can be further narrowed for better performance of the material. In this work, the cold work levels were varied in the range of 16% to 24%. Creep tests were carried out at 923 K and 973 K. There was no significant change in rupture lives with increase in PCW at 973 K. Increasing the level of prior cold work increased the rupture life significantly at 923 K. TEM studies revealed extensive recovery of the samples tested at 973 K. Samples tested at 923 K showed that extensive precipitation retained dislocation substructure.