Element Transfer Behaviors of Fused CaF 2 -SiO 2 -MnO Fluxes Under High Heat Input Submerged Arc Welding
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merged arc welding (SAW) has been widely applied in heavy industrial applications due to its high deposition rate. Such versatile technology joins metal by the heating of electrode, base metal (BM), and flux in the arc, while the weld metal (WM) is protected under molten slag.[1] Mn is one of the most essential elements for optimized WM mechanical properties, particularly for low carbon steel grades. Evans et al.[2] concluded that the increase of Mn from 0.6 to 1.8 wt pct enhanced the mechanical properties of the WM by promoting the formation of acicular ferrites and reducing polygonal and side plate ferrites. Harrison et al.[3] found that Mn increased the fraction of acicular ferrites by depressing the austenite to ferrite transformation temperature. In addition to
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 the School of Metallurgy, Northeastern University and also with the Department of Engineering, University of Leicester, Leicester LE1 7RH, UK. CONG WANG is with the 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 December 13, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Mn, Si, and O are also fundamental elements in WM; Si should be finely controlled as excessive Si, higher than 0.6 wt pct, may cause reductions in both elongation and toughness of the WM[4]; O influences final microstructure and mechanical properties of the WM by controlling inclusions characteristics and transformation products.[5] For SAW flux design, MnO is added to micro-alloy the WM with Mn or depress the Mn lost from the weld pool as a direct result of slag-metal chemical reactions[6,7]; furthermore, MnO may influence the transfer of Si and O by affecting the O potential of the flux[8] and the activity of SiO2.[9] In this regard, an understanding of the roles of MnO in controlling the element transfer behaviors between slag and weld pool during SAW is essential for a finely controlled WM compositions, which, in turn, determines the desired mechanical properties of the WM.[10,11] Effort was exercised to investigate the effect of MnO in flux on the behaviors of element transfer between slag and WM in SAW. Chai[4] postulated that, for a given element, there was a ‘neutral point’ for each flux where no element transfer between WM and slag could occur; he carried out ‘neutral points’ of Mn for several manganese-silicate type fluxes. Chai and Eagar[12] also designed binary CaF2-MnO fluxes and concluded that the transfer of Mn and O to the weld metals (WMs) was enhanced with increasing MnO content in the fluxes. Indacochea et al.[13] developed FeO-SiO2-MnO ternary fluxes and discussed the effect of MnO (and FeO) content on the transfer of elements in terms of thermodynamic drivin
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