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

Abstract

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.