Notch Tensile Properties of Various Regions of Dissimilar Joints of Austenitic and Ferritic Steels

In sodium cooled fast breeder reactor at Kalpakkam, the steam generators are constructed using modified 9Cr-1Mo (also called as Grade 91 or P91) ferritic steel because of its high temperature strength and resistance to stress corrosion cracking. The interconnecting sodium piping between reactor and steam generator is made up of AISI 316LN because of its high creep strength and corrosion resistance. Nickel based fillers (Inconel 82/182) are commonly used to weld the 316LN piping with steam generator. For a better structural integrity assessment of this dissimilar joint, the tensile properties of each region need to be evaluated. Evaluating the tensile properties of various regions by smooth tensile specimens is quite complex and time consuming. In the present investigation, the notch tensile properties of various regions were evaluated by placing a notch at the desired locations of the dissimilar metal weld joint (DMWJ). The dissimilar joint between P91 and 316LN is fabricated by manual metal arc welding (MMAW) process using Inconel 182 electrodes. Notch tensile properties of each region were evaluated by placing a notch at different locations (viz. weld metal, buttering, HAZ of P91 and HAZ of 316LN). Microhardness variation across the DMWJ was recorded. Microstructural features of various regions were characterized by optical and scanning electron microscope. From this investigation, it is found that the notch placed in the HAZ of P91 exhibited highest notch tensile strength than other regions. A non-uniform hardness distribution is observed across the DMWJ and the maximum hardness is recorded at the interface between P91 HAZ to Inconel 182 buttering. The hardness is minimum at the outer edge of HAZ of P91 side. Evolution of carbon enriched hard zone at the interface between P91 and Inconel 182 buttering could be the reason for highest notch tensile strength.