Dissimilar welding of austenitic and ferritic steels using nickel and stainless-steel filler: Associated issues

The microstructure development and mechanical behaviour of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed in this review paper. Nuclear reactor components, such as steam generators and pressure vessels, consist primarily of SA508 due to their low cost and high operating temperatures and pressures. The welding of dissimilar metals is crucial due to variations in physical characteristics such as thermal conductivity, thermal expansion coefficient, mechanical properties and chemical compositions. The principal challenges of dissimilar ferritic and austenitic steel welding are the subject of this review work. Weldability issues include a sharp change in mechanical and metallurgical characterization across the fusion line, carbon migration, cyclic thermal stresses and residual stresses, which necessitate a thorough investigation of the welded joint. Generally, austenitic steel and nickel-based fillers are used to join austenitic and ferritic steel materials; however, owing to many weldability concerns, nickel-based consumables are replacing austenitic consumables. Another critical issue in the weld joint is the selection of appropriate welding consumables, and detailed explanations of the benefits of employing a buttering layer on the ferritic side are provided. The effect of heat treatment on the metallurgical and mechanical characteristics of the weld joint, as well as the formation of residual stress, has also been thoroughly explored.