Austenitic stainless steels (ASS) are widely used in industries due to their excellent corrosion resistance and mechanicalproperties. Traditionally, nickel (Ni) is the key alloying element that stabilizes the austenitic phase in stainless steels, but recent trends areshifting towards the use of reduced nickel content. Manganese (Mn) and nitrogen (N) have emerged as replacements for nickel, leading tothe development of austenitic grades like the 200 series, particularly grade 202, which offers high hardness, strength, and corrosionresistance at a reduced cost. However, the sustainability of austenitic steels, especially in aggressive environments, remains a challenge.Duplex stainless steels (DSS), which combine ferritic and austenitic phases, may offer a cost-effective alternative with improved properties.This review explores the challenges of dissimilar welding between martensitic P91/P92 steel and austenitic stainless steel, focusing on theirapplication in Ultra Super Critical (USC) power plants. The review covers the mechanical behavior, microstructural issues, and weldabilitychallenges such as hot cracking, carbon migration, and formation of brittle intermetallic compounds. The role of filler metals, post-weldheat treatment (PWHT), and the effects of precipitate coarsening are also discussed. Finally, the potential for composite welds combiningduplex and austenitic steels is highlighted for improved strength and corrosion resistance, offering new opportunities in high-performanceapplications.Keywords: Austenitic stainless steel, duplex stainless steel, dissimilar welding, P91/P92 steel, Ultra Super Critical power plants,weldability, hot cracking, nickel substitution, manganese, nitrogen, post-weld heat treatment (PWHT), microstructure, precipitates, fillermetals, corrosion resistance, mechanical properties.