Experimental Investigation on Flux Activated TIG Welding of Different Steels

Abstract

In tungsten inert gas (TIG) welding, limited depth of penetration can be achieved during single pass welding. To achieve the desired depth of penetration, speed of welding needs to be significantly reduced and hence, productivity decreases. So to increase the productivity, the new technique was developed. In this technique an activated flux was used. The present work is an attempt to investigate the effect of activated flux and different gas shielding on weld morphology, mechanical properties, microstructure, microhardness of different graded steel (AISI 1020, AISI 304, AISI 316, Duplex 2205) at different currents and with different shielding gas compositions (pure Ar, Ar+5% H2 and Ar+He) during A-TIG welding. Fourteen fluxes are used in the present study for A-TIG welding. After experiments with these fourteen fluxes, it is found that five fluxes i.e. TiO2, SiO2, MoO3, MoS2 and CrO3 fluxes produce maximum depth of penetration and reduces depth-to-width ratio. It is also finding that the small percentage of H2 in the Ar shielding gas dramatically increase the depth of penetration up to 200% to 300%. So, based upon these results five fluxes are selected to carry out further study. Then parametric study is conducted to investigate the influence of five different fluxes, current, gas flow rate, vertex angle of electrode, and torch angle on joint bending load, toughness, microhardness. This study is carried out at two different welding speeds and under the two different shielding environments (i.e. 2 mm/s for Ar and 3 mm/s for Ar+5% H2). From the result of microstructure it is found that fluxes do not deteriorate the mechanical properties and sufficient austenite is found in the fusion zone from the transformation of austenite from ferrite but the use of 5% H2 in Ar shielding gas produce some porosity in the weld zone. It is also found that penetration increases significantly with increase of current during A-TIG welding. During ATIG welding with Ar shielding gas environment, maximum bending load (22.6 kN) is obtained when welding is carried out with TiO2 flux, 175 A current. Higher level of current (175A), higher gas flow rate and 60° tip angle helps to obtain higher bending load of the welded joints. During A-TIG welding with Ar+5% H2 shielding gas environment, maximum bending load is obtained when welding is carried out with MoO3 flux, 150 A current, 60° tip angle and 85° torch angle. In case of A-TIG welding with Ar shielding gas environment, maximum toughness is achieved when welding is carried out with CrO3 flux, 175 A current. In case of A-TIG welding with Ar+5% H2 shielding gas environment, maximum toughness is achieved when welding is carried out with SiO2 flux, 175 A current. Hence, higher current helps to achieve higher toughness value. Lathy and skeletal type δ-ferrite is also finds in some A-TIG welded samples. Maximum value of microhardness (446.147 HVN) in the FZ is obtained in case of Ar shielding, with SiO2 flux at 125 A (low current) and in case of Ar+5% H2 shielding the maximum microhardness (444.77 HVN) is found with CrO3 flux at 125 A current.