Influence of Gas Mixtures in GMAW of Modified 409M Ferritic Stainless Steel

The present study describes in detail the effect of shielding gas mixtures on the bead geometry, microstructure, and mechanical properties of gas metal arc welded modified ferritic stainless steel (409M) sheets (as received) of 4 mm thickness. The welded joints were prepared under spray (S) mode of metal transfer at same heat input using 308L austenitic filler metal and four different shielding gas mixtures, i.e., pure Ar, Ar + 5% CO2, Ar + 10% CO2, and Ar + 20% CO2. The welded joints were evaluated by means of microstructural changes, hardness, tensile strength, and toughness. The dependence of weld metal microstructure on shielding gas mixtures has been determined by bead geometry, Cr-eq/Ni-eq ratio, M-s, M-epsilon s, optical microscopy (OM), transmission electron microscopy (TEM), and electron probe microanalyzer (EPMA). It was observed that the variation in shielding gas mixture effectively manipulates the solid-state phase transformation and precipitation behavior of the welded joints. Variations in microstructure ultimately affect the mechanical properties of the weld metal as well as coarse-grained HAZ (CGHAZ). The present study concluded that up to 10% CO2 may be commercially utilized in the shielding gas mixture for fabricating waded joints of 409M using 308L filler metal without deteriorating microstructural and mechanical properties.