The current study investigates the effect of some welding electrodes and post-weld heat treatment (PWHT) on tensile strength, hardness, impact energy, and microstructural transformations of mild steel weldments, using the shielded metal arc welding (SMAW) technique. Four different electrode specifications were used in this study, these includes cast iron (AG4700), mild steel (E6014), stainless steel (E308L-16), and mild steel (E6013) electrodes. Eight (8) samples of mild steel plate of length 100mm and 5mm thickness were first sectioned and welded across the width using the four electrodes (2 samples per each). After welding, four of the welded plates with each of the four different electrode materials were then subjected to the post-weld heat treatment (Normalizing) at a temperature of 8000C, soaked for 50 mins, and then allowed to cool naturally in an open-air. Both the heat-treated and the as-welded samples were then subjected to various mechanical tests. The result obtained showed that the welds with mild steel electrodes (E6013 and E6014) possess higher tensile strength for both the heat-treated and untreated welds, while the AG4700 electrode gave the highest impact energy after thermal treatment as compared to other welds. The hardness values with all the four electrode materials were generally found to decrease after post-weld heat treatment. The microstructural results revealed the breaking of the original fine grain structures in the as-welded condition to more coarser structures after heat treatment for all the weldments, which appears to account for the lower hardness obtained in the post-treated steel welds. Based on the results obtained, it can be concluded that some electrode materials impart adequate mechanical properties in the as-welded condition, while some, depending on the type of mechanical properties to be improved, require post-weld heat treatment on the weldment.
Key words: Electrode materials, post-weld heat treatment, mechanical properties, microstructures, SMAW process
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