Trimetallic weld joints between Grade‐91, Alloy‐800, and SS316LN steels are used at the steam generator inlet of prototype fast breeder reactors. In this configuration, dissimilar welds between ‘IN82 buttered Grade 91 steel and Alloy 800’ welded with IN182 electrode, are susceptible to premature creep failure. This vulnerability arises from microstructural degradation in Grade 91 adjacent to IN82 caused by thermo‐mechanical effects during buttering, welding, and post‐weld heat treatment. The resulting heat‐affected zone exhibits strong heterogeneity in microstructure, which produces a graded strain field that conventional uniaxial creep tests cannot capture. In this study, digital image correlation is used to map strain evolution and failure in cross‐weld Grade 91 flat subsize specimens tested at 550°C under stresses of 250–325 MPa, and to relate strain localization to microstructure. Strain evolution is highly inhomogeneous across the heat‐affected zone, with local peak strains exceeding 20% in the intercritical heat‐affected zone (ICHAZ), while average strains remain below 5%. Results identify the ICHAZ as the weakest region and the coarse‐grained HAZ as the most creep‐resistant. Rejuvenation of the ICHAZ by reducing precipitate depletion and martensite tempering is expected to improve creep life.
Suman et al. (Thu,) studied this question.