Sigma Embrittlement Evaluation Test for Dissimilar Welding Between F6NM and FXM-19

Abstract In dissimilar welds between martensitic stainless steel F6NM and nitrogen-strengthened austenitic stainless steel FXM-19, type 209 austenitic welding materials is used to match the mechanical properties and chemical composition of FXM-19. The welds of F6NM must be subjected to Post-Weld Heat Treatment (PWHT) to restore ductility and toughness. Therefore, sigma embrittlement is a concern for ER209 buttering welds as they are subjected to PWHT. In this research, the mechanical properties and microstructure of dissimilar welds of F6NM+FXM-19 were investigated. There was no significant difference in the volume fraction of sigma phase between the buttering weld metal (PWHT) and the groove weld metal (As weld) for each welding process. Therefore, sigma phase transformation by PWHT did not occur. Submerged Arc Welding (SAW) and Gas Metal Arc Welding with 100%Ar gas shield (GMAW 100%Ar) were found to have good mechanical properties. In Gas Tungsten Arc Welding (GTAW), the impact value was below the required value in the Charpy impact test of the buttering weld metal. SAW and GMAW 100%Ar were found to be applicable welding processes for this dissimilar weld joint.