Laboratory report on experiment using GMAW on mild steel Harshita Rathod 210110090 Nameofthestudent:Pranav Harshita Rathod 210110090 Salunke Roll Number:210110085 Objective of the experiment: • To study the effect of heat input on the bead geometry using GMAW process. • To do metallographic polishing on the welded specimens provided and carry out through microstructural characterization of the weld joint of any one of the geometries. Experimental Observations alumel type thermocouple Nature of thermocouple used = Chromal alummel Max Voltage and current of the transformer = 30V, 300A Geometry of the welded joint = T joint 3.15mm diameter Dimensions of the filler rod = 3mm Observations and results: Comment on the difference between SMAW and GMAW . SMAW A SMAW electrode has an external flux covering (because of it is called stick welding) SMAW can leave slag deposits on the weld surface due to the vaporizing flux Utilizes thick flux coated electrode. Apart from protecting the electrode, this flux supplies shielding gas. Electrode ought to be replaced frequently due to the short length Lower filler deposition rate GMAW GMAW electrode has an external shielding gas GMAW enables greater efficiency because it produces cleaner welds There is no flux coating for the electrode. To prevent oxidation of the electrode materials, a thin covering of a substance is applied No need for frequent replacement of the electrode and longer welding time Higher filler deposition rate and more productive Include optical micrographs and identify the regions of HAZ after careful etching of the specimens. Add a micron marker to the micrographs and measure the approximate thickness of various zone and justify the results. 50 microns BASE METAL 50 microns HAZ 100 microns 100 microns Macrostructure of the Weld • • • • • Two identical Mild Steel (MS) plates are welded together For mild steels, the carbon content usually is around 0.25 - 0.50 wt % Fusion Zone is where the liquid phase exists in the phase diagram Partially Melted Zone (PMZ) exists where the liquid phase exists in equilibrium with the solid phase Heat Affected Zone (HAZ) exists where the base metal undergoes a solid phase transformation Insert the necessary parameters as given in the table below and comment on the effect of heat input on the width of the fusion zone, width of the HAZ and height of the reinforcement. From the figure we can see heat input significantly affects bead geometries by influencing the bead width and perform depth. The increase with an increase in heat input. The amount of fused weld material has likely increased, which is the likely cause of the rise. Reinforcement Height also increases with the increase in heat input. Ref - https://www.tandfonline.com/doi/full/10.1080/23311916.2016.1143598 Brief explain the experimental observation and justify the results: From micrograph we can observe the grains in the HAZ are bigger in size than base metal which is due to heating of metal above the recrystallization temperature and cooling of the HAZ region slowly which gave rise to larger sized grains. So we conclude grain size differ with varying cooling rates.
