A critical review on dissimilar welding of ferritic-martensitic steel and austenitic stainless steel using gas tungsten arc welding process: Weldability issues, processing, and performance characteristics of joints

This study presents a critical review on the dissimilar welding of ferritic-martensitic steel (FMS) and austenitic stainless steel (ASS) using the gas tungsten arc welding (GTAW) process. The problems in dissimilar welding of FMS and ASS, such as hot cracking, cold cracking, carbon migration, delta-ferrite formation, and Type-IV cracking are discussed in detail. The effect of joint design, filler wires, welding techniques, and technologies in the GTAW process on the evolution of microstructure, mechanical properties, creep behavior, corrosion resistance, and residual stress distribution of dissimilar FMS/ASS joints is critically reviewed and discussed. The effect of postweld heat treatment (PWHT) cycles and high-temperature long-term ageing conditions on microstructure, mechanical properties, and creep behavior of joints is also reviewed in detail. The results showed that the multipass GTAW joints of FMS/ASS made using nickel/Inconel-based filler wires offer a good combination of tensile strength, ductility, and WM toughness compared to autogenous GTAW and activated flux GTAW joints. However, the issues of detrimental unmixed zone and softer delta-ferrite phase formation, development of migrated grain boundaries, alloying segregation, and carbon migration can be observed in the joints. Also, it shows less response to PWHT due to the stable austenitic WM microstructure. The non-conventional PWHT involving normalizing and tempering is effective in enhancing the WM toughness and creep life of joints compared to the conventional PWHT involving only tempering. This principally corresponds to the full precipitate dissolution during normalizing and the precipitation of secondary phases after tempering. Thus, the findings of this review article provide significant insights into the weldability and performance characteristics of dissimilar FMS/ASS joints and highlight the need for process parameter optimization and effect study to improve the performance of these joints. The FMS/ASS joints find applications in high-temperature and highly corrosive regions of power plants. This necessitates in-depth research work on the high-temperature properties of joints.