Investigation on the mechanical properties of weld metal using the modified submerged arc welding flux

This study investigates the feasibility of utilizing modified welding flux, which was recycled from submerged arc welding (SAW) slag. Four groups of modified flux samples were prepared by blending commercially available KF-550 submerged arc flux with recycled welded slag. These samples were subsequently employed in the SAW of A36 low-carbon steel. The research focused on analyzing alterations in the chemical composition and phase evolution of the modified flux, as well as evaluating the alloy composition and mechanical properties—including tensile strength and impact toughness—of the resulting weld metals. The incorporation of soluble glass (sodium silicate) as a binder in the modified fluxes introduced SiO2 and MgAl2O4 into the compositions, which affected the viscosity of the molten flux and the effectiveness of protective gases. Consequently, the weld metals exhibited reduced silicon (Si) and manganese (Mn) contents, resulting in decreased tensile and yielding strengths but improved impact toughness. The fully recycled flux, sample S100, characterized by the highest manganese oxide (MnO) content, reacted with carbon to generate carbon monoxide (CO) gas. This gas can locally provide a reducing atmosphere, which contributes to weld pool protection, facilitates the incorporation of Mn into the weld metal, and further reduces the Si content. The findings suggest that silicon content in the weld metal has a more significant influence on impact toughness than manganese content.