Studies on Creep Deformation and Rupture Behavior of 316LN SS Multi-Pass Weld Joints Fabricated with Two Different Elect
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TYPE 316 LN austenitic stainless steel (SS) is the prime structural material for fabricating components of the Prototype Fast Breeder Reactor (PFBR) which is in the advanced stages of commissioning in Kalpakkam, India.[1] Its superior elevated temperature mechanical properties and corrosion resistance have been widely demonstrated, and there is immense international experience regarding the usage of this material in fast breeder reactors (FBR).[2] Welding is indispensable while fabricating large components of FBRs which are made from this alloy. Although exhaustive studies have been made on the creep deformation and rupture properties of the austenitic steel weld metal,[3–7] there is limited literature dealing with the mechanical properties of the composite V.D. VIJAYANAND, J. GANESH KUMAR, P.K. PARIDA, and V. GANESAN, Scientific Officers, and K. LAHA, Head of Mechanical Metallurgy Division, are with Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Homi Bhabha National Institute, Kalpakkam 603102, India. Contact e-mail: vdvijayanand@ igcar.gov.in Manuscript submitted 21 March 2016. Article published online November 15, 2016 706—VOLUME 48A, FEBRUARY 2017
weld joint which is more realistic to assess.[8–11] Understanding the creep rupture behavior of austenitic stainless steel weld joints is pivotal to evaluate the design life of FBR components. Life predictions of the components with weld joints are usually made using the data obtained by testing wrought materials incorporating a strength reduction factor.[12] The main cause of this strength reduction is the microstructural instability in the fusion zone. The heterogeneity in microstructure makes interpreting the associated damage due to creep exposure all the more complicated. Assessing the cause for the microstructural heterogeneity in the fusion zone can facilitate design of welded joints with better mechanical properties. A major cause of microstructural inhomogeneity is the change in the morphology of delta ferrite during fabrication of multi-pass weld joint.[13] Delta ferrite of 3-8 FN in fusion zone is intentionally introduced through the adjustment of chemical composition to avoid hot cracking. The work by Horton and Li[8] showed that the variations in delta ferrite content and morphology across the short transverse direction of the fusion zone are the prime sources for scatter in creep properties of type 316 SS fabricated by shielded metal arc (SMA) welding process. They had shown that the METALLURGICAL AND MATERIALS TRANSACTIONS A
scatter in rupture data considerably reduced with increasing the specimen thickness. It was also pointed out that the specimen size in relation to the weld bead size also influenced the rupture life of the joint. They had concluded that the weld joint specimen should encompass significant number of weld beads to average out the effect of variations in delta ferrite content and its morphology. Recent studies on the creep properties of 316LN SS weld joint showed that variation in delta ferrite morphology di
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