Study on Flux assisted-Tungsten inert gas welding of bimetallic P92 martensitic steel-304H austenitic stainless steel using SiO2–TiO2 binary flux

Abstract

In present work, flux assisted-tungsten inert gas (FA-TIG) welding of bimetallic P92 martensitic steel-304H austenitic stainless steel (ASS) is carried out using SiO2–TiO2 binary flux. Seven binary fluxes were prepared by varying the proportions of flux powders (SiO2 and TiO2) and the effect of flux composition on weld bead cross-section was studied. The experimental results indicated that binary flux (flux B) with composition 90% SiO2 + 10% TiO2 yields the most pronounced effect on weld bead cross-section with 289.9% improvement in the depth of penetration (DoP) and 58.48% reduction in weld width (WW) in comparison to TIG (no flux) weld joint. To understand the potential mechanisms (arc constriction and reversal of Marangoni's convection) account for improved weld bead cross-section, the efficacy of flux compositions on welding arc/pool behavior is discussed in detail. The addition of a little quantity of TiO2 (10%) in SiO2 (90%) flux helped in achieving the narrowest arc (arc diameter: 5.40 mm), the maximum increase in arc voltage (ΔV = 2.14 V) and an increase in nascent oxygen amount (151 ppm) in the weld pool as compared to TIG (no flux) welding, which confirmed the occurrence of both arc constriction and reversal of Marangoni's convection. The weld joint developed using optimized binary flux (flux B) possessed untempered lath martensite, prior austenite grain boundaries, ferrite stringers and equiaxed austenite grains in the various zones of the weld joint. The average hardness of the weld zone was obtained as 415.9 HV. The developed weld joint qualified the tensile test with ultimate tensile strength (UTS) 680.9 MPa, yield strength (YS) 340.5 MPa and elongation 31.4%.