Changes in Microstructural and Mechanical Properties of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel on Lo
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LIQUID sodium is used as coolant in liquid metal-cooled fast breeder reactors (LMFBRs), because of its excellent nuclear and heat transfer properties and good compatibility with structural materials.[1] Intermediate heat-exchanger (IHX) and steam generator are the main components in the secondary circuit of prototype fast breeder reactor (PFBR), under construction at Kalpakkam in India. The material of construction selected for the IHX is AISI type 316LN SS in view of N. SIVAI BHARASI, Scientific Officer D, M.G. PUJAR, Leader, Environmental Degradation & Monitoring Program, K. THYAGARAJAN, Scientific Officer D, C. MALLIKA, Head, ACSCS, and U. KAMACHI MUDALI, Associate Director, are with the Corrosion Science and Technology Group (CSTG), Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam 603 102, Tamil Nadu, India. Contact e-mail: [email protected] ANURADHA DHAUL, Scientist, is with the Solid State Physics Laboratory, Defense Research and Development Organization, Delhi 110 054, India. M. NANDAGOPAL, Scientific Officer E, CSS, MMD, and A. MOITRA, Scientific Officer G, MMS, MTD, are with the Materials Development and Technology Group (MDTG), Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu, India. S. CHANDRAMOULI, Head, ROS, and K.K. RAJAN, Director, FRTG, are with the Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu, India. Manuscript submitted February 28, 2015. Article published online September 15, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
its adequate high-temperature mechanical properties, compatibility with liquid sodium, good weldability, availability of design data, good irradiation resistance, and above all vast and satisfactory experience in the use of similar steels in sodium-cooled reactors elsewhere in the world.[2–5] For the steam generator of PFBR, modified 9Cr-1Mo steel is used, as this material provides good high-temperature mechanical properties, resists the loss of carbon to liquid sodium, does not undergo wastage in case of small leaks leading to sodium–water reaction, and offers resistance to stress corrosion cracking (SCC) in high-temperature caustic solutions.[6] Corrosion of structural materials of LMFBRs in high-temperature liquid sodium poses a unique problem due to a wide range of factors such as solubility of metals and non-metals in sodium, thermophysical condition of the structural material, temperature of exposure, Down-Stream Effect, axial rate of heating of sodium, residual stress on materials, temperature differential in the loop, velocity of sodium, etc. The overall sodium corrosion damage in structural materials includes dissolution of material, mass transfer, and deposition of alloying elements. The extent of mass loss due to leaching of alloying elements leading to a general wall thinning, selective leaching of alloying elements, and formation of surface ferrite layer and carburization/ decarburization occurring in liquid sodium depends on VOLUME 46A, DECEMBER 2015—6065
the purity of sodium and chemica
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