Microstructural investigation and mechanical properties evaluation using miniature specimen testing of various constituents of dissimilar weld joint

Microstructural evolution in P91 (modified 9Cr–1Mo) steel and 316LN Stainless Steel (SS) bi-metallic weld joints fabricated by arc welding technique using Inconel-182 electrode has been studied in as-welded and post weld heat treated (PWHT) conditions. The PWHT brought about significant changes in the microstructure which altered the strength gradient especially in the ferritic steel side. The differences in weld thermal cycling which occurred in various regions of the P91 steel side caused M23C6 precipitates to evolve in varying sizes. The size variation in these precipitates was the paramount cause for the variation in strength in this region which could be probed by miniature specimen testing. Using this testing it could be established that PWHT resulted in offsetting the strength variation in the HAZ of the ferritic steel side. It could also be understood that PWHT generates a weak region in the P91 side making it most susceptible to damage.