Variation of Mechanical Properties across the Dissimilar Joints: Ferritic steel and Stainless Steel

Abstract

Grade 91 ferritic steel (also known as P91) is widely used for constructing steam generators in prototype fast breeder reactors (PFBR) because of their stress corrosion cracking resistance, high thermal conductivity and low thermal expansion co-efficient for intermediate heat exchangers and austenitic stainless steels (SS304L, SS316L and SS316LN.) Due to their high temperature creep strength and good corrosion resistance, the dissimilar metal weld (DMW) joints between these materials are unavoidable. Inconel 82/182 filler metal is recommended to join these materials since its thermal expansion co-efficient lies between that of ferritic steel and stainless steel. In the present investigation, the tensile properties of each region of DMW joint have been evaluated. DMW joint between P91 and SS 316LN were fabricated using manual metal arc welding (MMAW) process with inconel 82/182 filler metals. The tensile properties of various regions of DMW were examined at a nominal strain rate of 1×10-3 s-1. Microstructural features of various regions of DMW were examined through optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Out of different regions, P91 parent metal exhibited higher tensile strength while the transverse tensile specimens failed at the outer edge of the HAZ of P91 steel. This heterogeneity in mechanical properties may be due to the evolution of complex microstructures developed during welding.