Effect Of Cold Work On Creep Behavior Of Ti Modified 14cr 15ni D9i Austenitic Stainless Steel

Abstract

Creep rupture strength and resistance towards irradiation-induced-void swelling are the newlineforemost qualifying criteria for the steel to be used for fabricating nuclear fuel clad tubes. newlineThe important life limiting factor for the steels used in the core of the fast breeder reactor newline(FBR) is void swelling due to neutron radiation leading to dimension distortions of the newlinestructure. Austenitic stainless steels are the preferred materials for high temperature newlinecomponents of FBRs. Alloy D9I (Ti-modified 14Cr-15Ni austenitic stainless steel) has newlinespecifically tailored chemical composition to resist void swelling during irradiation of the newlineFBR core, which experiences temperature as high as 700 °C and intense neutron flux that newlinegenerates point defects such as vacancies and interstitials leading to void swelling in the steel. newlineCold work enhances the void swelling resistance by introducing more number of dislocations, newlinewhich act as sink for the point defects to recombine and annihilate. The addition of silicon, newlinephosphorus, and boron also improves the void swelling resistance of the steel. The addition newlineof titanium is advantageous because during creep exposure, fine TiC precipitate at newlinedislocations and help in enhancing creep resistance in addition to reducing the void swelling newlinein the steel. newlineCreep rupture behavior of D9I alloy, indigenously developed at IGCAR Kalpakkam, was newlinestudied in current investigation. Solution annealed, 10, 20, 30, and 40 % cold worked (room newlinetemperature) conditions of the steel were studied for creep behavior at 700 °C and at various newlinestress levels. Microstructure evolution during cold working and post creep exposure has newlinebeen discussed in detail. newlineDuring cold working, dislocations were generated and stored in the form of low angle grain newlineboundaries or subgrain boundaries. Increase in cold work level resulted in prominent low newlineangle grain boundaries and led to denser dislocation network in the sample. Low angle newlineboundary fraction increased as the amount of cold working increased to 40 %. Tensile strength as well as hardn