Microstructures and Mechanical Properties of 304 Stainless Steel Joints by Focused Ultrasound-Assisted TIG Welding

The microstructure and mechanical properties of focused ultrasound-assisted TIG welds on 304 stainless steel were investigated. Compared with TIG welding, the weld depth and depth-to-width ratio of focused ultrasound-assisted TIG welding were increased by 200 and 256%, respectively. The microstructures of the focused ultrasound-assisted TIG weld were composed of austenite (98.3%) and ferrite (1.7%), and the ferrite content was higher than that of TIG welding (0.7%). The average grain size of focused ultrasound-assisted TIG weld was 32.8% smaller than that of TIG. The tensile strength and elongation of the focused ultrasound-assisted TIG joint were 764.3 +/- 18.1MPa and 66.3 +/- 3.4%, respectively, which were higher than the tensile strength (729.3 +/- 6.8MPa) and elongation (60.3 +/- 1.2%) of TIG welding. Due to the compression of arc and the stirring of the molten pool by focused ultrasound, the efficiency and penetration of focused ultrasound-assisted TIG welding were improved. The grains were refined, and the mechanical properties of joints were improved.