Microstructure and mechanical property assessment of hot wire TIG and activated TIG hybrid weld joint of AISI 316L(N) stainless steel

Abstract

A 12-mm-thick AISI 316L(N) steel plate was welded using a hybrid technique that combines hot wire tungsten inert gas (HWTIG) and activated tungsten inert gas (A-TIG) processes. The microstructure and mechanical properties of the hybrid joint were systematically compared with those of multi-pass HWTIG and single-pass A-TIG welds. The hybrid weld metal contained 7% delta ferrite, sufficient to suppress hot cracking susceptibility. The average hardness values of the weld metal were 170 VHN for HWTIG, 175 VHN for A-TIG, and 180 VHN for the hybrid joint. The cross-weld tensile strength of the hybrid weld joint (580 MPa) closely matches that of the HWTIG (605 MPa) and A-TIG (575 MPa) joints, indicating that all three welding techniques achieve similar strength levels under tensile loading. Charpy impact toughness values were also similar across the three processes (HWTIG: 155 J, A-TIG: 140 J, Hybrid: 150 J). Fracture toughness of the hybrid joint was appreciable at both room temperature (410 kJ·m⁻²) and 550 °C (155 kJ·m⁻²), aligning closely with HWTIG (400, 170 kJ·m⁻²) and A-TIG (395, 165 kJ·m⁻²). Overall, the HWTIG + A-TIG hybrid welding technique produced joints with acceptable microstructure and mechanical performance, demonstrating its potential for application in welding thick sections of nuclear reactor components.