The mechanical behaviors of shield-ed metal arc welding (SMAW) of butt joint of mild steel

Abstract

Mechanical behaviours/properties are the most important engineering considerations in manufacturing, design, and constructions of products. These manufacturing usually involve assembling and joining of the components and parts to form a complete product. One of the widely used metal joining method is fusion welding method. In this study, mechanical behaviours of Shielded Metal Arc Welding (SMAW) of mild steel were studied. Welding works were performed using current, voltage and polarity parameters. Investigations of tensile testing, impact testing, hardness testing, and microstructure examination of welded mild steel have been conducted. The relation between ultimate tensile strength (UTS) and current shows a fluctuation pattern. Increasing current does not increase UTS proportionally. UTS also does not proportional with voltage. Furthermore, for correlation of UTS and current relative to polarity, the UTS for DCEN polarity were observed to be higher than UTS for DCEP polarity. For voltage from 23 to 24 volts, the UTS for DCEN polarity were higher than the UTS for DCEP polarity. However, as the voltage increase from 26 to 27 volts, the UTS for DCEP polarity eventually become higher than the UTS for DCEN polarity. In order to achieve high UTS and tensile strength, one should choose current from 68 to 120 ampere combined with voltage of 23 volts. For maximum toughness, high current ranged from 102 amperes to 120 amperes should be used with voltage varied from 24 to 26 volts in DCEN polarity. The microstructure of the weld metal shows a combination of ferrite and pearlite grain structure which signifies that the welded materials exhibit in brittle and ductile behaviors correspondingly. Three positions of indentation were used to measure the hardness of the welded materials which are fusion zone, heat affected zone (HAZ) and base metal zone. Among those three, the hardness properties at the fusion zone are the highest for most samples tested. The hardness was also observed to be highest when the current is 70 amperes. The hardness was found to be directly proportional to the voltage values.