Element Transfer Behaviors of Fused CaF 2 -SiO 2 Fluxes Subject to High Heat Input Submerged Arc Welding
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nt years, to further improve welding efficiency, submerged arc welding (SAW) with higher heat input has been widely applied.[1–3] SAW relies on appropriate fluxes to obtain satisfactory weld metal (WM) properties.[4] Generally, flux is employed in SAW to stabilize the arc, add alloying elements, and refine WM microstructure.[5] To better control WM composition and offer acceptable mechanical properties, an understanding of element transfer mechanisms between slag and weld pool during welding is necessitated.[6] Tremendous effort has been exercised to investigate the transfer behaviors of certain elements during SAW. For instance, Dallam et al.,[7] by performing SAW with CaF2-CaO-SiO2 system fused fluxes on Nb-containing high-strength low-alloy (HSLA) steels, studied the transfer of Si and Mn, and pointed out Si is transferred to the WM when the mass ratio of SiO2 and CaO in flux is greater than one. Chai et al.[8] investigated the effect of several CaF2-based binary flux formulas on the
JIN ZHANG and CONG WANG are with the School of Metallurgy, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] THERESA COETSEE is with the Department of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria 0028, South Africa. Manuscript submitted August 19, 2019.
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compositions of the WMs and concluded that most oxides tend to decompose and improve O level of the WM in SAW. Burck et al.,[9] on the other hand, offered detailed investigations over the effect of CaF2, CaO, and FeO additions into manganese-silicate-based fused fluxes on the transfer behavior of Si, Mn, and O. However, one essential and complicated issue is that the metal-transfer mode is highly influenced by welding parameters, especially heat input, which puts forward a challenge on the composition control of the WM.[10,11] For high heat input SAW, characterizations of inclusions, microstructure, and mechanical properties of the WM have been extensively studied, but attempts to investigate element transfer behavior exceeding heat input of 20 kJ/cm remain scarce.[8,10,12–16] The aim of this work is to systematically investigate the effect of SiO2 on the transfer of O, Si, and Mn under high heat input SAW. When a flux is designed, SiO2, acting as network-builder, is added indispensably to improve slag detachability and bead morphology;[17] CaF2 plays the role of minimizing the O potential and melting temperature of the flux. In this regard, a series of fused CaF2-SiO2 binary fluxes targeted for high heat input (60 kJ/cm) SAW are developed. A typical shipbuilding steel plate, EH36, has been selected as the base metal (BM).[18] For SAW, despite departures from the equilibrium, it is accepted that the state of equilibrium is attained locally due to the large surface-to-volume ratio and high temperature in the confined volume.[4] As a consequence, thermodynamic considerations are applied to place constraints on chemical reactions and element transfer mechanisms in the present study. As a flux
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