An approach to tunable advanced high-strength steel fabrication through multi-wire arc additive manufacturing (M-WAAM)

Advanced high-strength steel (AHSS) fabrication through conventional casting followed by thermomechanical processing always sets challenges for the research community in terms of weldability (microstructural degradation during welding) and formability (high wear of forming dies). Considering such limitations, multi-wire arc additive manufacturing (M-WAAM) has been developed that houses two feedstock (ER70S-6 and 316L stainless steel (SS)) on a single gas metal arc welding (GMAW) power source. Here, both filler wire feed speeds (WFS) are monitored and controlled through an autonomous wire feed system (AWFS), leading to simultaneous melting for fabricating the near-net-shaped alloy structure. In the developed alloy, the proportion of 316L SS is varied by regulating its WFS between 0 and 1.5 m/min, whereas WFS for ER70S-6 is fixed at 2 m/min. With the increase in WFS of 316L SS, the deposition volume and alloying element concentration increases, whereas the penetration depth decreases with smooth side wall and negligible molten metal overflow, indicating adequate utilisation of developed heat for wire melting. Moreover, the ferrite-pearlite microstructure is transformed into ferrite, bainite, and martensitic structures by increasing the secondary WFS, as evident from microstructural and X-ray diffraction analysis. The development of multiple phases further boosts the mechanical performances (hardness and tensile strength) of deposits. Also, the mechanical strength offered by these fabricated alloys is in the range of AHSS steels.