Dissimilar IN82 Buttered P91 and Incoloy 800HT Joint for AUSC Boilers: Microstructural Characteristics and Mechanical Properties

This work explores the microstructural and mechanical characteristics of a dissimilar metal weld (DMW) between P91 steel and Incoloy 800HT. The P91 heat-affected zone (HAZ) was observed for the significant changes in the microstructure. The micro-mechanical analysis helped in revealing the effect of microstructural features observed on the mechanical properties. The P91 HAZ had an observable effect of multiple thermal welding passes on the microhardness variation in the region. The application of buttering during the welding process provided a partial alternative to the need for post-weld heat treatment. The P91 HAZ displayed the presence of a high number of dislocation densities. The welded regions were analyzed using electron backscatter diffraction (EBSD). The weld fusion zone (WFZ) was observed with dendritic structures having grain orientation alignment in the <111> direction. The solidified buttering layers and WFZ exhibited a complete face-centered cubic (FCC) structure. The solidified region was also observed with minor recrystallization. The tensile tests of the DMW specimens demonstrated ductile mode of failure at room temperature. During high-temperature tensile testing, specimens demonstrated the flow stress anomaly. The ultimate tensile strength for the DMW at room temperature was recorded at 665 MPa. During Charpy impact toughness testing, the WFZ exhibited a ductile mode of failure with a Charpy impact toughness of 87 ± 5 J.