Correlating Microstructure with Mechanical Properties for Different Regions of Dissimilar Metal-Welded Joints

In light water reactor of nuclear power plant, welded joint between dissimilar steels requires sufficient
reliability, ample efficiency, substantial operational life, and adequate safety. In the present investigation,
welded joints were produced between low alloy steel (SA 508 Gr.3 Cl.2) and 304LN austenitic stainless steel
(SA 312 Type 304LN) using INCONEL 82 (IN82) as both buttering material and weld metal. For one set of
joint, a post-weld heat treatment was carried out at pre-defined parameter. Owing to wide difference in
characteristics of these alloys, microstructural and mechanical properties exhibited substantial variation at
different regions of welded assembly. Portable automated ball indentation (PABI) technique was used to
evaluate the mechanical properties of various zones across the welded joint. Quantitative assessment of
microstructural features of the joint was performed by conventional microscopy and x-ray diffraction
technique and electron backscattered diffraction. Across fusion boundary, it was observed that the weakest
region was buttering material. The reason of low strength was attributed to low dislocation density, minimal
KAM value, and small microstrain along with moderate crystallite size. Strength of all zones across the
joint was reduced after heat treatment; however, the failure prone location was still within buttering
material. In this context, PABI with x-ray diffraction and EBSD experimentation endorsed the potential of
the combined technique for reliable evaluation of dissimilar metal-welded joint.