Comparative study of physical and mechanical properties of A36 mild steel welded joints using oxyacetylene and shielded metal arc welding processes

Abstract

One of the crucial industrial methods for joining metals has been welding, hence many techniques have been developed to get an efficient and cost-effective process for different kinds of materials. In this study, an attempt was made to investigate the tensile and bending strength of A36 2.5 mm thick mild steel plate welded by the processes of oxyacetylene and shielded metal arc welding (SMAW). The specimen, having been carefully welded to form butt and lap joints were subjected to tensile and bending tests using universal testing machine WAW-1000H. Four test runs were performed for each welded joint. Based on the results obtained from the tensile and bending tests conducted, it was observed that oxyacetylene welded joint produced a stronger joint that could withstand much higher force compared with shielded metal arc welded joint when lap and butt joints were considered. Where in oxyacetylene lap welded joint, an average maximum ultimate tensile strength of 332.75 N/mm2 under an average force of 83.188 KN was obtained for four sample specimen, shielded metal arc lap welded joint, recorded an average maximum ultimate tensile strength of 288.5 N/mm2 under an average force of 72.125 KN. For butt joint, oxyacetylene recorded an average tensile strength of 288.75 N/mm2 under an average load of 72.125 KN as against 256.75 N/mm2 under an average load of 64.163 KN for shielded metal arc welded joint. However, in considering bending strength of oxyacetylene butt and lap welded joints and shielded metal arc butt and lap welded joints where the joined workpiece might be subjected to bending working conditions, shielded metal arc butt and lap joints recorded bending strength of 6.0 N/mm2 under an average force of 0.6 KN and 6.50 N/mm2 under an average force of 0.65 KN for butt and lap joints respectively as against 5.88 N/mm2 under an average load of 0.59 KN and 6.38 N/mm2 under an average load of 0.64 KN for oxyacetylene welded butt and lap joints respectively. It is therefore recommended to welding practitioners, engineers and fabricators that, for tensile strength, using 2.5 mm thick mild steel plate, oxyacetylene butt and lap welded joints should be used compared to shielded metal arc butt and lap welded joints as the former could withstand much higher tensile strength than than the later. However, for bending strength, shielded metal arc butt and lap welded joints appears slightly beneficial than the other.