Effect of shielding gases on microstructure and mechanical properties of super austenitic stainless steel by hybrid welding

This paper investigates the bead geometry, microstructure and mechanical properties of AISI 904 L super austenitic stainless steel joint by CO2 laser–GMAW hybrid welding process. Shielding gas is one of the important parameters for the process stability and efficient synergetic effects between laser and gas metal arc welding (GMAW). A detailed study of CO2 laser–GMAW hybrid welding with different shielding gas mixtures in different ratio (50%He + 50%Ar, 50%He + 45%Ar + 5%O2, and 45%He + 45%Ar + 10%N2) was carried out on AISI 904 L super austenitic stainless steel sheet of 5 mm thickness. The weld penetration of hybrid welding was determined by the plasma shape varying with the shielding gas parameters, especially the plasma height interacting with incident plasma. The X-ray diffraction was used to analyze the phase composition, while the microstructural characterization was performed by phase microscopy of the joints. The impact and tensile tests were performed and fracture surface morphology had been analyzed through scanning electron microscope (SEM). Finally, hardness test is performed along the longitudinal direction of the weld zone. The results showed that the joint by laser–GMAW hybrid had higher tensile and impact strength than the base metal. The fractrography observation showed the cup-cone shaped fracture while the hybrid welding joint mixed mode of fracture. The laser–GMAW hybrid welding is suitable for welding of AISI 904 L super austenitic stainless steel owing to their high welding speed and excellent mechanical properties.

► The laser–arc hybrid welding has the better gab bridgeability.
► The full penetration is achieved without any defects like porosities.
► 50%He + 45%Ar + 5%O2 shielded weld joints increment approximately 36% compared to base metal.
► The 50%He + 45%Ar + 5%O2 hardness values are higher. The tensile strength is less in 50%He + 50%Ar shielded weld.