Assessment of Creep Strain Distribution Across Base Metal of 316LN Austenitic Stainless Steel Weld Joint by an EBSD-Base
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INHOMOGENEOUS distributions of accumulated plastic strain are frequently encountered in most of the load-bearing components. The source of the inhomogeneity could be welding which results in the formation of microstructurally different zones with varying mechanical properties, leading to inhomogeneous stress distribution on loading. It could also be due to geometrical irregularities within the components, resulting in a non-uniform distribution of stress which consecutively develops strain gradients during service. Although life assessment of the components through microstructural study is quite popular, the measurement of accumulated strain can be a useful method of estimating remnant life of component. Electron back scatter diffraction (EBSD) is a promising tool to estimate the accumulated plastic strain. The correlation
V.D. VIJAYANAND, V. GANESAN, and J. GANESH KUMAR, Scientific Officers, P. PARAMESWARAN, Program Leader of Structure Property Correlation Programme, and K. LAHA, Head of Mechanical Metallurgy Division, are with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. Contact e-mail: vdvijayanand@igcar. gov.in NAVEENA, formerly Senior Research Fellow with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, is now Project Research Scientist with the Graduate School of Science and Engineering, Kagoshima University, Kagoshima Japan. Manuscript submitted December 3, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
of the estimated plastic strain with creep exposure may be a more useful way of estimating remnant life. Parameters obtained from EBSD have been previously used to measure the plastic strain in austenitic stainless steel to assess the stress corrosion cracking in high temperature aqueous environment.[1] This technique has also been used to study the excessive plastic deformation which leads to initiation of cracks in grade 316 austenitic stainless steel subjected to low-cycle fatigue.[2] Likewise, it has been demonstrated by several researchers that EBSD can be effectively used to estimate the plastic strain.[3–8] Type 316LN austenitic stainless steel is a primary structural material of liquid metal-cooled fast breeder reactors.[9] Welding is the primary fabrication process employed for construction of various components of the reactor. These welded components will be subjected to temperatures up to 923 K (650 C) for their envisaged design life of 40 years. Microstructural stability of the material for such long durations, which would assure the optimum performance of the components, is of paramount importance. In austenitic steels weld joints, the weld metal is considered to be the weakest region. The delta ferrite which is intentionally allowed through compositional adjustment of the weld metal to inhibit hot cracking during welding process, transforms into intermetallic phases during creep exposure, leading to brittle failure of the joints at high operating temperatures. There are many studies describing the microstr
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