Investigation of Microstructure Evolution in Wire Arc Additive Manufacturing of Steel Followed by Hot Forming

Abstract

Metal Inert Gas (MIG)-based weld deposition process, a subset of wire arc additive manufacturing (WAAM), has received significant attention in the field of additive manufacturing (AM). This technique is favored for its ability to efficiently produce complex, dense and fully functional metallic components. Its key benefits include high deposition rates, material and energy efficiency, lower investment costs, and simplified setup requirements, making it an attractive option for metallic AM. This study focuses on exploring the synergistic effects of combining two processing practices: additive manufacturing and hot forming with varying hammer strokes (3HS, 5HS, and 7HS) on steel components. The investigation utilizes the WAAM technique with a MIG setup to create components on a low alloy steel substrate, employing diverse deposition patterns. Experiments were conducted using fully automated MIG welding on a low alloy steel substrate with ER70S-6 copper-coated steel wire. Samples were built using five different deposition patterns: longitudinal, transverse, right network, oblique, and oblique network. To evaluate the samples, various examinations were performed, including optical microscopy and scanning electron microscopy. The results revealed that the samples built with the different deposition patterns showed a diversity of microstructure in different regions along the cross-section of the additives. Microscopy generally showed that the primary constituent of the dominant structure in the additive material was lamellar pearlite with grain boundary ferrite, accompanied by a smaller fraction of ferrite grains. Hot forging led to a notable reduction in the interlamellar spacing within the pearlite colonies, and in both grain boundary ferrite and ferrite grains across the additives.