Effect of Mild Steel Butt Welded Root Opening on Speed, Hardness, Root Penetration, discontinuity and Tensile Strength by using E7018 Welding Electrode

Abstract

The weldability of E 250 mild steel plates which are extensively used in penstock pipes of hydropower depends upon different parameters like welding current, voltage, travel speed, electrode angle and root opening. Mostly, E7018 electrode is used for welding by Shielded Metal Arc Welding (SMAW) process. Root opening is the gap between the two metals in a butt joint that are to be welded. Four sets of samples are prepared by fitting two samples each of 300 mm length x 300 mm width x 10 mm thickness with root opening of 2 mm, 4 mm, 6 mm and 8 mm respectively with bevel angle of 60 degrees, single groove and root face of 2 mm. The welding speed decreased from 81.31 mm/min, 76.23 mm/min, 66.58 mm/min to 55.54 mm/min at root opening for these samples respectively. Hardness of the material indicates the changes in property of the material after being welded. The hardness in weld metal increased from 125.6 HV, 127.3 HV, 136.8 HV to 139.2 HV and hardness in heat affected zone increased from 104.3 HV, 106.8 HV, 107.7 HV to 108.6 HV for these samples respectively. Complete root penetration of 10 mm was found while welding in root opening of 4 mm whereas minimum root penetration of 8.8 mm, 8.1 mm and 6.9 mm was found while welding with root opening of 2 mm, 6 mm and 8 mm respectively. The root penetration decreased with an increase of root opening. As, the experiment is carried in constant current and voltage, the heat input required for 6 mm and 8 mm root opening is less causing less root penetration in welds. There is no effect in minimum required tensile strength of welded zone and the rupture is found to be in parent metal in all those samples.