Influence of filler metals and PWHT regime on the microstructure and mechanical property relationships of CSEF steels dissimilar welded joints

The nuclear grade modified 9Cr-1Mo (P91) and 9Cr-0.5Mo-1.8W-V-Nb (P92) are commonly used material for power plant components operating in the temperature range of 600-650 degrees C. For such steels, the creep strength at the elevated operating temperature is the prime criteria. However, microstructure stability and notch toughness also play an important role, especially for the welded joints to meet the pressure test at room temperature. The room temperature mechanical properties of the welded joint are strongly influenced by the welding process, filler composition, composition of the base plate and heat treatment performed after the welding. In present work, P91 and P92 dissimilar multi-pass welded joints have been produced using the different filler rod. The microstructure of the welded joint has been studied for the different filler composition in various heat treatment condition. The room temperature Charpy impact toughness and tensile properties for the different welded joints (different filler) have been also studied and related with the microstructure of the welded joint. From the results, it has been concluded that a higher amount of ferrite stabilizer in P92 filler promotes the formation of the 8 ferrite in the weld fusion zone.