Fig. 1 — Weld preparation and test plate assembly. and decreases the maximum droplet detachment frequency. The shielding gas not only affects the metal transfer but also determines the shape and penetration pattern. Several researchers have investigated the effect of CO2 content on weld penetration with the variation in welding parameters and found that the weld penetration increases with the CO2 content (Refs. 7, 8). The influence of shielding gas composition on the apparent weld shape as well as on the surface tension of the droplet travel between the electrode tip and weld pool were also studied (Refs. 9, 10). It appears that the shielding gas is one of the key factors that ultimately affects the microstructure and mechanical properties of A B C the welds, mainly through the mode of metal transfer. However, available information concerning the effects of Ar and CO2 shielding gas mixtures on the dissimilar weld joint of 409M ferritic stainless steel welded with 308L filler metal is very meager. Hence, it becomes imperative to study both from an economical as well as technical point of view the effect of an increase in CO2 content in a binary Ar-CO2 mixture under spray mode, on the microstructural and mechanical properties of welded joints. In the present study, ferriticaustenitic dissimilar welds (409M base plate and 308L filler metal) are made by varying the shielding gas mixture, namely pure Ar, Ar + 5%CO2, Ar + 10% CO2, and Ar + 20% CO2, under spray mode of metal transfer. The aim of the present work was to study the effect of various mixtures of Ar and CO2 on the solid-state phase transformation, precipitation behavior, and mechanical properties of the GMA welded joints. Experimental Procedure Material The hot-rolled sheets of 4-mm-thick 409M grade ferritic stainless steel were cut into required dimensions and used for the gas metal arc welding (GMAW) process. The details of weld joint preparation and test plate assembly are shown in Fig. 1. The chemical composi- WELDING RESEARCH 102-s WELDING JOURNAL / APRIL 2015, VOL. 94 Fig. 2 — Schematic view of the different locations of the welded joint considered in graphical measurement of the area of weld deposit (AWD) and the area of base metal fusion (ABF). Fig. 3 — Dimensions. A — Unnotched tensile specimen; B — notched tensile specimen; C — subsize impact specimen. Table 1 — Chemical Compositions of Base Metal and Filler Metals Type Chemical Composition (in wt%) SSP 409M Base metal C% Si% Mn% P% S% Cr% Ni% Mo% Cu% Nb% N% 0.030 0.463 0.79 0.029 0.014 11.10 0.31 0.033 0.026 0.017 0.01 308L Filler Metal 0.015 0.53 1.68 0.012 0.03 19.53 9.26 0.117 0.082 0.026 0.053
Welding Journal | April 2015
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