Characterization of Welded Joints of Similar and Dissimilar Metals with Various Processing Routes

Abstract

In this work, an attempt has been made to join IS 2062 mild steel plates for similar metal welding and both IS 2062 mild steel and AISI 409M stainless steel plates for dissimilar metal welding by various processing routes i.e. gas metal arc welding (GMAW) and shielded metal arc welding (SMAW) in both straight polarity and reverse polarity. The dimensions of the plate used for welding in both similar and dissimilar metal were taken as length of 100 mm and breadth of 50 mm as per ASTM standard. For similar metal welding process, the thickness was varying from 5 mm, 6 mm and 8 mm, respectively and for dissimilar metal welding only 8 mm thickness was considered. In both welding process, the input current was considered at 120 A, 140 A and 160 A, respectively. The welded samples were vigorously investigated with various zones by using of various universal testing machines. The microstructural analysis of welded samples was carried out by using optical microscope and scanning electron microscope (SEM) of various zones i.e. fusion zone, heat affected zone (HAZ) to analyze the grain sizes changing with various process parameters. Maximum grain size of 17.09 μm was observed in metal coarsening zone and minimum grain size of 5.43 μm was investigated in grain refinement zone of welded mild steel plates with the application of 160 A current on 8 mm thick plates in SMAW straight polarity welding. In the X-ray diffraction pattern the peaks of α-ferrite were observed, at 2θ values of 52.30˚, 77.17˚ and, 99.65˚, respectively of the welded samples for both GMAW and SMAW processes. All the x- ray patterns for the welds at different current and different plate thicknesses were studied. But all of them yielded the same profiles with no variations at all. From hardness study it was found that maximum hardness was observed in the grain refinement zone of each process and with an observation of increasing in hardness while increasing current. Tensile test was conducted and observed that optimum tensile strength of 387.879 MPa was found in GMAW process by the application of 160 A current on 5 mm thick material. To determine the toughness of the joint, impact test was conducted and maximum toughness of 180.728 J/cm2 was noticed with the application of 120 A current on 8 mm thick plates in GMAW process. In dissimilar metal welding, the materials were welded by variations of welding current with consideration of 8 mm thick plates with various processing routes like GMAW and SMAW (Reverse polarity). Then the microstructural and mechanical characterizations of welded specimens were examined. In microstructural study maximum coarse grains in metal coarsening zone and fine grains in grain refinement zones were observed in GMAW processes due to more efficiency of heat inputs on work piece. Fe-Ni intermetallic, Fe carbides and Fe-Cr solid solution were investigated through X-ray diffraction study in GMAW and SMAW processes for the dissimilar metal welding. Maximum hardness of 543.8 HV was observed in case of SMAW process in fusion zone with application of 160 A current. Optimum tensile strength of 365.15 MPa was investigated in case of GMAW process with application of 120 A current. From impact test study it was investigated that maximum impact toughness of 178.28 J/cm2 was observed in case of GMAW process with application of 120 A current.