Microstructural analysis of preheated 1020 low carbon steel agglutinated at predetermined wire feed rates using the FCAW process

Abstract This study examined the impacts of sample temperatures (32, 100 and 150 °C) and wire feed rates (2.5, 5, and 10 m/min) on bead geometries as well as microstructural characteristics of 1020 steel plates with 10 mm thickness, using Flux-cored Arc Welding (FCAW) process. The findings revealed that higher preheat temperature resulted in wider beads and deeper penetration owing to slower cooling rates, whereas higher wire feed rates (WFR) produced lengthy bead height, with varied penetration depth. Shallow and optimal penetration depth were observed for 2.5 and 5 m/min WFR, while excessive material deposition was noticed for 10 m/min, which limited the penetration depth. Consequently, finer grain structures were noticed around fusion zones at lower preheat temperatures and WFR, whereas grain transition from fine to coarse structures slowly occurred around the HAZ, migrating towards the base metal. However, while higher WFR yielded intense heat input and coarser grains, wider HAZ with more uniform grain size distribution were observed for higher preheated temperatures. The statistical metrics via standard deviation revealed microstructural variations characterized by coherent grain refinement and ferrite-pearlite distributions, demonstrating uniform molten pool dynamics, homogeneous cooling rates and optimal thermal gradients across the HAZ.