Parametric Study on Flux Activated Tungsten Inert Gas Welding of AISI 316 and Duplex 2205 Steel

Abstract

Joining of thin plate (~ 2–3 mm) by Tungsten Inert Gas (TIG) welding gives satisfactory results in terms of depth of penetration but for relatively higher thickness plates the speed of welding should be reduced to achieve desired penetration that lowers productivity. So, to increase the depth of penetration at reasonable good welding speed some oxide powders are used. These oxide powders are mixed with acetone and are applied on the plate before welding. These oxide powders cause higher depth to width ratio and as a result of this the materials get joined through all its thickness properly. This process of TIG welding when oxide flux is used is called Activated TIG (ATIG) welding. The purpose of this research work is to study the effects of specific fluxes used in the TIG welding on joint strength by analyzing impact strength, variation of microhardness and bending when two similar graded austenitic stainless steel plates are welded together. This process is repeated for two materials i.e. AISI 316 of 6 mm thickness and Duplex 2205 of 7 mm thickness. Plates were prepared with the edge groove at an angle of 45º. Filler rods with 3 mm diameter are made of AISI 316 and Duplex 2205. The torch was given a constant speed of 1.3 mm/s and constant height of 3 mm with the help of self made cart setup. There were three varying currents 125 A, 150 A and 175 A and three different gas flow rates 10 L/min, 13 L/min and 16 L/min with different torch angles 50º, 70º and 90º with the horizontal. Two different gases (pure Ar and Ar + 5% H2 ) were used as protecting gases and three different oxide powders TiO₂, MoS₂ and SiO₂ mixed with acetone (flux) is applied on the steel plates before welding. After welding, toughness and bending test were carried out to study the mechanical strength of the joints. The results indicate that SiO₂ and TiO₂ fluxes lead to a significant increase in the depth penetration capability of TIG welds. The activated TIG process can increase the joint penetration and maximum bending load was found using SiO₂ flux with higher gas flow rate. Use of TiO₂ flux provided higher toughness of the welded joints. Higher bending load was achieved when Ar + H2 is used as shielding gas as compared to pure Ar.