Effect of Mild Steel Coated with Locally Formulated Flux as Electrode on the Microstructure and Tensile Properties of Arc Welded Joint

Abstract

The microstructure and tensile properties of arc welded joint of medium carbon steel using locally formulated low hydrogen flux coated on mild steel as electrode(s) was investigated. The electrodes were formulated using commercial low hydrogen flux (E7018) partially replaced with titanium dioxide, potassium fluoride (KF) and potash extracted from locust bean seed pod (KLBSP) which was enriched with sodium silicate in varying compositions. The electrodes produced were coded as E1, E2, and E3. The welding was carried out at 75A rooting and 115A capping current using direct current electrode positive (DCEP) and direct current electrode negative (DCEN) polarities. The electrode core diameter size of 4mm was employed for the welding. The analogue Avery universal testing machine with maximum load 250 kN was used to determine the tensile properties while microstructure examination was carried out at 400X magnification using optical microscope N 400 POL. The results from tensile properties using electrode coded E1 and E2 using DCEN had yield strength (YS) of 510.33 N/mm2 and 471.67 N/mm2, while ultimate tensile strength (UTS) were 548.67 N/mm2 and 501.33 N/mm2 respectively. These values compare closely with UTS of welded joints made of E7018 electrode which has an average value of 480 N/mm2 and 570 N/mm2 for YS and UTS respectively. Whereas welded joints made from electrodes coded E1, E2 and E3 using DCEP had values of 262.50 N/mm2, 230.33 N/mm2 and 404.00 N/mm2 respectively for YS and 288.67 N/mm2, 262.33 N/mm2 and 431.00 N/mm2 respectively for UTS. Based on this study, the recommended polarity to be employed for welding using the formulated electrode is the DCEN using electrode coded E1 and E2.