Submerged arc welding (SAW) is a highly efficient welding technique that is well suited to joining thick materials due to its ability to achieve high deposition rates. Its reliability and scalability make it widely applicable across various industries. This paper presents an innovative method to enhance the mechanical properties of weld metal by incorporating manganese-functionalized boehmite nanoparticles into the SAW process. The research systematically investigates the influence of welding parameters—arc voltage, current, electrode stick-out, welding speed, and nanoparticle-layer thickness—on the hardness and microstructure of the weld zone in St37 steel. The findings reveal that the inclusion of manganese-adsorbed boehmite nanoparticles significantly improves weld-zone performance. Under the welding-arc heat, these nanoparticles decompose into aluminum oxide and manganese oxide, contributing to increased hardness and mechanical strength while promoting notable grain refinement. This transformation alters the weld microstructure from coarse ferrite to fine acicular ferrite, improving toughness and resilience. Using response surface methodology, optimal welding parameters are identified, with hardness as the primary response variable. The results show that higher welding speeds and greater electrode stick-out increase hardness, while excessive arc voltage and current lead to grain coarsening and reduced hardness. The presence of nanoparticles further increases hardness, achieving a peak value of 152.15 HV (Vickers hardness) with a 1-mm-thick nanoparticle layer compared to a baseline hardness of ∼140 HV in nanoparticle-free samples. Microstructural analysis confirms a roughly 30% reduction in grain size, highlighting the critical role of nanoparticles in refining microstructure and enhancing the mechanical properties of the weld.

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