It is well known that, the major limitation of conventional short circuiting gas metal arc welding process (GMAW) for welding of various ferrous and non-ferrous materials is poor bridgeability and generation of large number of spatters. To overcome these difficulties, in recent years, waveform controlled technology has been introduced in GMAW process for specific application to meet required quality and productivity. However, the specific advantage of the process for various welding application primarily depends on the waveform parameters such as peak current, background current, time and voltage. It is often found that, irregular control of waveform leads defects like porosity, undercut and burn through etc. which impairs the weld joint quality. Thus, it is very important to study the effect of different waveform on bead geometry and microstructure. In this regard, in the present investigation aimed to carry out various waveforms on root pass welding of carbon and alloy steels. The bead appearance, soundness, macro and micro structure analysis has been carried out. Based on the results the optimum range of waveform has been derived and appropriately correlated with process parameters. © 2017 Elsevier Ltd.