Role of ultrasonic vibration in improving metallurgical integrity and mechanical strength of dissimilar SS304/316 TIG welds

The present study is aimed to examine the impact of ultrasonic vibration during welding on the microstructural behavior and mechanical properties of dissimilar austenitic stainless steel SS304/SS316 TIG welds. The 10 mm thick double-sided V-grooved SS304/316 plates were fabricated with ER318 filler using both conventional TIG welding and vibration-assisted TIG welding. Welding parameters, i.e. welding current 120 A and voltage 14 V, were kept constant, and vibration power (0–500 W) and frequency (20 and 40 kHz) were systematically varied. The microstructural analysis revealed that the coarse columnar dendrites fragmented into fine equiaxed grains as a result of acoustic cavitation and streaming during vibration. With increased frequency and power of vibration, refinement increased, and at 40 kHz, 500 W, the microstructure was dominated by equiaxed grains, as confirmed by both scanning electron microscopy and EDS. X-ray diffraction analysis revealed a stable weld-zone microstructure dominated by γ-austenite and minor δ-ferrite retention. The UTIG weld zone revealed up to 23% enhancement in the micro-hardness and up to 36% enhancement in absorbed energy due to vibration.