Element Transfer Behaviors of Fused CaF 2 -TiO 2 Fluxes in EH36 Shipbuilding Steel During High Heat Input Submerged Arc
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merged arc welding (SAW) is widely applied for the welding of thick steel grades due to its inherently high deposition rate.[1] During SAW, no shielding gas is required as the weld pool is protected by a layer of molten slag and granular flux from atmospheric contamination.[2] Flux is the primary source of O for weld metal (WM), and flux basicity is an indirect indication of the flux O potential.[3–6] Generally, higher flux basicity means lower flux O potential and better mechanical properties, especially low-temperature toughness.[7,8] Among several flux categories, basic-fluoride fluxes are widely
JIN ZHANG is with the School of Metallurgy, Northeastern University, Shenyang 110819, China. THERESA COETSEE is with the Department of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria, 0002, South Africa. HONGBIAO DONG is with School of Metallurgy, Northeastern University and also with the Department of Engineering, University of Leicester, Leicester LE1 7RH, UK. CONG WANG is with School of Metallurgy, Northeastern University and also with the State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] Manuscript submitted May 28, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
applied to achieve excellent mechanical properties as the addition of CaF2 improves basicity and minimizes flux O potential.[5,9–13] In recent years, to further improve mechanical properties or counter toughness deterioration of the weld under high heat input welding, TiO2, a typical acicular ferrite (AF) promoting component, is introduced into basic-fluoride fluxes.[11,14–16] As such, Ti and O are transferred to the WM via chemical reactions in the arc and weld pool zones.[11,13,17] Subsequently, Ti-containing inclusions are dispersed, AF formation is facilitated, and the enhancement of mechanical properties of the weldment is anticipated.[18] When TiO2-bearing basic-fluoride fluxes are applied, it is essential to understand the roles of TiO2 in the control of WM compositions to ultimately achieve desired mechanical properties.[11,14,19] Several authors investigated the effects of TiO2 content in varying basicfluoride fluxes over a wide range of WM compositions. For instance, Kohno et al.[14] developed CaF2-SiO2BaO-Al2O3-TiO2 fluxes, which could transfer Ti and O to the WMs via the reduction of TiO2 in the fluxes, concluded that the Ti content in the WM increased with lower flux potential. Roy et al.[20] investigated the influence of TiO2 content on WM compositions employing CaF2-SiO2-MgO-Al2O3-MnO-TiO2 fluxes, and found that the Ti level of the WM was promoted with TiO2 addition from 0 to 12.5 wt pct. Zhang et al.,[11] on the other hand, performed SAW using CaF2-SiO2Al2O3-MgO-TiO2 fluxes with varying TiO2 addition from 1 to 16 wt pct, and revealed that WM Ti content reached a maximum when 6 wt pct TiO2-containing flux was applied. However, the studies reviewed above only considered WM’s change in final compositions, in which the elemental contribution from the
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