Optimizing the Friction Welding Parameters to Maximize Tensile Strength of Sus 304HCu Austenitic Stainless Steel Tube Joints

The SUS 304HCu austenitic stainless steel is used in superheater / reheater of ultra super critical boilers for their high temperature oxidation and corrosion resistance. Cu addition to steels can have adverse effects on the mechanical properties during fusion welding as it can form low temperature eutectic phases that preferentially segregate to the grain boundaries and embrittle the alloy. Friction welding is a solid state welding process where the bonding takes place well below the melting temperature of the alloy, combined with the autogenous nature of this welding process minimizes the adverse effects of low temperature eutectics segregation. Hence, in this investigation an attempt has been made to develop an empirical relationship to predict the tensile strength of the friction welded SUS 304HCu tubes of 57.1 mm outer diameter and 3.5 mm thick using statistical tools such as design of experiments, analysis of variance and regression analysis. Response surface methodology was used to optimize the process variables and maximum joint efficiency of 99% was achieved using the optimized friction welding variables.