Productivity improvement in butt joining of thick stainless steel plates through the usage of activated TIG welding

Activated tungsten inert gas (A-TIG) welding is one variant of conventional TIG welding where a thin layer of suitable activating flux is deposited on the parent components prior to constituting the arc in order to harness enhanced penetration. Despite several benefits, industries are still reluctant in overwhelmingly using this new variant. This article attempts to highlight the productivity benefits in employing A-TIG welding either together with or superseding TIG welding during butt joining of 10-mm-thick AISI-316L austenitic stainless steel components. Initially, three single-component fluxes (Cr2O3, Fe2O3, and SiO2) are tested in forehand welding technique under varying currents but with straight polarity. Filler rod having similar metallurgical composition is also delivered during homogeneous welding. The extent of capability of each of the three fluxes is analysed by comparing the weld bead geometrical parameters (penetration, puddle width, and reinforcement) with the same obtained in conventional TIG welding under similar set of parameters. While Fe2O3 and SiO2 fluxes are found capable in enhancing penetration and reducing puddle width and heat affected zone, Cr2O3 flux failed to exhibit better performance. The article further demonstrates the time saving that can be obtained by adopting flux-assisted TIG for joining 10-mm-thick plates. When joining from both the faces is allowed, about 70% less time is desired if a combination of A-TIG and TIG is employed rather than using only TIG welding. If joining from only one face is allowed, then also usage of flux can reduce welding time by 33%.

Influence of Metallic Oxide Nanoparticles on the Mechanical Properties of an A-TIG Welded 304L Austenitic Stainless Steel

Austenitic stainless steels represent a significant aerospace material, being used for various castings, structural components, landing gear components, afterburners, exhaust components, engine parts, and fuel tanks. The most common joining process is tungsten inert gas (TIG) welding, which possesses many advantages such as suitability to weld a wide range of ferrous and non-ferrous metals and alloys, providing high quality welds with good mechanical properties. Its major disadvantage is low productivity due to low penetration and welding speed. This can be overcome by introducing an activating flux before welding. The activating flux reverses the material flow of the weld pool, significantly increasing penetration. Therefore, shielding gas consumption is reduced and welding without a consumable is enabled. However, the consumable in conventional TIG also enables the conditioning of the mechanical properties of welds. In this study, Si and Ti metallic oxide nanoparticles were used to increase the weld penetration depth, while bend testing, tensile, and impact toughness were determined to evaluate the mechanical properties of welds. Furthermore, optical emission spectroscopy, light, and scanning electron microscope were used to determine the chemical compositions and microstructures of the welds. Chemical compositions and weld mechanical properties were similar in all specimens. The highest tensile and impact properties were obtained with the specimen welded with the flux containing 20% TiO2 and 80% SiO2 nanoparticles. Although lower than those of the base metal, they were well within the nominal base metal mechanical properties.