UNDERSTANDING CREEP DEFORMATION BEHAVIOR OF 316LN STAINLESS STEEL AND ITS WELD JOINT USING IMPRESSION CREEP TECHNIQUE By NAVEENA Enrollment No.: ENGG02200804029 Indira Gandhi Centre for Atomic Research, Kalpakkam A thesis submitted to the Board of Studies in Engineering Sciences In partial fulfillment of requirements For the Degree of DOCTOR OF PHILOSOPHY of HOMI BHABHA NATIONAL INSTITUTE November, 2013