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Wire Arc Additive Manufacturing (WAAM) is being explored as an alternative to casting components for large steel structures such as bow and stern sections of hull structures. This study investigated t...he appropriate process window for WAAM using gas metal arc welding (GMAW), employing pure CO₂ as the shielding gas and mild steel wire intended for structural steel applications, and evaluated fundamental aspects of mechanical properties and microstructure. WAAM deposition was performed under various heat inputs and mid-length surface temperatures (MLST). Microstructural observations revealed fine blocky ferrite at mid-height due to repeated heat inputs, while the top layer exhibited grain boundary ferrite and acicular ferrite typical of weld metal. Hardness was slightly higher near the substrate and the top layer compared to the middle part. Within the tested range, variations in heat input and MLST had minimal influence on bead geometry, hardness, and microstructure. Tensile tests on specimens extracted from a large deposited wall showed no significant difference between horizontal and vertical directions, indicating isotropic mechanical properties. Differences in microstructure at each position were explained by temperature histories obtained through finite element analysis and associated phase transformation behavior. These findings provide fundamental insights into WAAM using GMAW using pure CO₂ welding for structural steel and its potential for large-scale applications.続きを見る
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