Dissimilar metal welding of P91 steel-AISI 316L SS with Incoloy 800 and Inconel 600 interlayers by using activated TIG welding process and its effect on the microstructure and mechanical properties

This study investigates dissimilar metal weldments between P91 steel and AISI 316 L austenitic stainless steel fabricated by activated TIG welding (A-TIG) with and without the use of interlayers of Incoloy 800 and Inconel 600. Through thickness penetration in 8 mm thick plates was achieved in a single pass A-TIG welding using a pre-coated mixture of metallic oxides. Hot cracking was eliminated in A-TIG weld joints in contrast to conventional TIG weld joints without flux. Fully martensitic structure was observed in the weld metal developed without the use of interlayer. Microstructural modifications were achieved with the use of interlayers. The weldment with Incoloy 800 interlayer exhibited martensitic-austenitic structure whereas fully austenitic structure was observed with Inconel 600 interlayer. Interlayers improved impact toughness and ductility of the weld joints without significant loss of tensile strength. The effect of interlayers on carbon migration after aging treatment (620 degrees C/500 h) was evaluated with the help of thermodynamic simulations and it was observed that the use of interlayers reduced the severity of carbon migration.