Effect of Welding Electrodes and Post-weld Heat Treatment on Some Mechanical Properties and Microstructural Transformations of Mild Steel Weldment using Smaw Process

Abstract

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 include 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). Following the welding operations, a post-weld  heat treatment (Normalizing) at a temperature of 8000C was applied to four of the welded plates with each of the four distinct electrode  materials, soaked for 50 minutes, and then allowed to cool naturally in the 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 of the welds with the four electrode materials were  generally found to decrease after post-weld heat treatment. The microstructural results revealed the growth of the original fine grain  structures in the as-welded condition into 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.