This work describes welding of the sheets with different thickness values and then characterizing the mechanical and microstructural properties for two different types of welding i.e. GMAW and SMAW. The joints are devised in such pattern that the effect of sheet thickness and welding current on these properties can be easily assessed. Initial microstructural studies are carried out with high-resolution optical microscopy and SEM. These images are then processed in ImageJ software to analyze various properties of different phases involved. Mechanical properties like the tensile strength, microhardness, impact energy or toughness are also measured and correlated with the microstructures and welding parameters. The main aim of this project is to design new set of welding parameters for structural steels that are used widely in different construction works and industries. Optimizing the results and choosing the best possible way to get superior properties are the key points.

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Welding has been done by taking mild steel as work piece material in shielded metal arc welding (SMAW) process. Material thickness and current were considered as input parameters. Joining of metals has been completed in two ways. In first process double pass welding has been done in which 1st pass was in reverse polarity and the second pass was in straight polarity and in the 2nd process both the passes of welding were completed with straight polarity. The comparison of microstructure and impact toughness has been investigated. It was found that more amount of heat was generated in the 2nd process as compared to the 1st process. Therefore, growths of grains in heat affected zone occurred and maximum growth occurred in 2nd than 1st process. Impact strength increased with decrease in current value and increase in material thickness respectively. The impact strength values for 1st process welding were relatively less as compared to 2nd process.

Abstract. In order to perform arc welding, mild steel plates of variable thickness i.e. 5 mm, 6 mm and 8mm has been chosen as parent material. Total nine numbers of experiments were conducted by considering the two factors and three levels of design according to Taguchi method. The welding current and material thickness has been selected as variable input parameters with 5mm, 6 mm, 8mm level of material thickness and 90 A, 100A, 110A level of current respectively. The microstructure of the all the nine welded material has been analysed with the help of an optical microscope which is interfaced computer. The results of microstructure obtained from the microscopic investigation have been shown. The effect of current and material on the weldment microstructure is investigated. The result also shows that the coarse structure is formed in fusion zone and fine structure is formed in Heat affected region.