A B and CaO-TiO2-SiO2 type ENiCrFe-7 (Refs. 8, 10, 11). Recently, a modified ENiCrFe-9 covered electrode has been developed that was designed especially for welding 9% Ni steel for construction of large-tonnage LNG ships. For improving the cryogenic impact toughness of the weld metal, both alkalescent and strong basic slag systems were adopted. In this paper, the modified ENiCrFe-9 covered electrodes with two different slag basicities were investigated in terms of the mass transfer coefficient, as-deposited microstructure, as well as the mechanical properties of the deposited metal. The influence of the flux coating on the welding performance, weld quality, and cryogenic impact energy were discussed. This research was part of the work to develop the ENi- CrFe-9 type covered electrode for industrial application. The role of the basicity of the flux coating was a focus of the investigation. One of the objectives of this study was to evaluate the mass transfer coefficients of the key elements in two different flux coating systems for developing ENiCrFe-9 type covered electrode for welding 9% Ni steel. The results could also provide valuable data for developing other types of nickel-based covered electrodes with pure nickel core. Experimental Procedure Because the alloy core wire was more difficult to produce, and had a higher electric resistance that could result in a quick temperature rise during welding (Refs. 7, 12), the commercial pure nickel with diameter of 3.2 mm and length of 350 mm was used as the core wire in this paper. In the pure nickel, the C is less than 0.05 wt-%, and the S and P are less than 0.015 wt-%, respectively. The other impurities are less than 0.5 wt-%. Some appropriate mineral powders used in the flux coating were selected in accordance with our own proprietary technology. Ingredients of the flux coating are listed in Table 1. The production process of the covered electrodes was carried out by using the conventional extrusion method. The as-extruded covered electrodes were baked at 423 K for 1 h and then 573 K for 1 h. The appearance of the core wires and the covered electrodes are shown in Fig. 1A. The 25-mm-thick 9% nickel steel plates (provided by the Nanjing Iron & Steel Group Corp.) were cut and machined to the size of 400 mm 200 mm 25 mm for the welding experiments. A single V-groove butt joint configuration with a 60-deg groove angle, together with a 13-mm root opening, was prepared — Fig. 2. Prior to welding, the base metal WELDING RESEARCH Alloy Covered Electrodes (wt%) 468-s WELDING JOURNAL / DECEMBER 2016, VOL. 95 Fig. 1 — A — Pure nickel wires and the covered electrodes produced for this study; B — the aswelded test plate; and C — the macro morphology of the deposited metal. C Table 1 — Flux Coating Ingredients of the NickelBased Type CaCO CaF TiO NaAlF SrCO 45% Si 28% Ti 56% Mo Mo Mn Cr 50% Nb 74% W 50% Al NaCO KOTi KO NaO SiO3 2 2 36 3 23 4422 2 + + + + + + 55% Fe 72% Fe 44% Fe 50% Fe 26% Fe 50% Mg CaF 17.8 20.0 – – – 2.2 3.0 4.4 3.0 6.3 25.5 7.0 1.5 – 0.6 0.5 2.0 0.7 5.5 2CaOSiO 2 TiO2SiO 2 7.5 – 12.0 11.9 4.0 2.5 2.5 6.1 2.7 6.7 26.5 6.2 1.6 0.7 0.4 0.5 2.0 0.7 5.5 SrO
Welding Journal | December 2016
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