Microstructural and mechanical analysis of directed energy-deposited mild steel

This study introduces a novel submerged arc additive manufacturing (SAAM) method that uses high-efficiency submerged arc plasma to produce large-scale low-carbon steel components with isotropic microstructures. Using submerged arc welding (SAW) with copper-coated electrode wire and AUTOMELT A55 flux, low-carbon steel parts were produced with high surface quality and dimensional accuracy. The parameters analyzed include the submerged arc welding technique, contact-tip-to-work distance, current and wire feed speed (WFS), welding travel speed, and heat input. The welded part underwent multiple reheating cycles due to the layer-by-layer manufacturing process. As a result, high temperature gradients at the beginning of the weld led to the formation of a fine grain structure. In contrast, as the part's height increased and the temperature gradient decreased, coarser grains were formed. By leveraging an in situ intrinsic heat treatment process (multi-layer-penetration normalizing, full-layer-penetration inter-critical annealing, and tempering), the method achieves a columnar-to-equiaxed grain transition, refining and homogenizing the microstructure layer by layer. Similar trends were obse