was polished with a grinding wheel and then cleaned with acetone. Butt joint welding in the flat position was performed by using shielded metal arc welding (SMAW). The alternating current was set to 125–130 A, the welding voltage was 23–25 V, the welding speed was 3.5–4.0 mm/s, and the interpass temperature was controlled below 393 K. To keep both ends of the weld at the same height, the welding of the next pass began at the end of the previous pass. Between passes, the weld bead was cleaned with a chipping hammer and stainless steel brush. Radiography was conducted to detect welding defects, and the results indicated that all the deposited metals were qualified. The appearance of the as-welded plate and the macro morphology of the deposited metal with about 45–50 passes were shown — Fig. 1B and C. The spatter loss coefficient, melting and deposited rates, slag detachability, and bead geometry were evaluated by using the methods described in Refs. 12–18. To collect the spatter, a 9% Ni plate with the dimension of 300 50 25 mm was erected on a copper plate weld interface with the thickness of 3 mm. Both the 9% Ni steel and the copper plate were put in a cylindrical box of copper with the height of 400 mm, diameter of 600 mm, and thickness of 1 mm for avoiding spatter loss. The spatter deposited on the plate in the box could be easily collected. The spatter loss coefficient, SLC was defined as SLC = Ms/Mw * 100% (1) where Ms indicates the weight of the spatters and Mw indicates the mass loss of the electrode. For each type electrode, three tests were conducted. The reported SLC is the average value of the three tests. The melting rate, MR, and the deposited rate, DR, are defined as the following equations: MR = MC/At (2) DR = Md/At (3) where MC indicates the mass loss of the core wire, Md indicates the weight of the deposited metal, A indicates the welding current, and t indicates the WELDING RESEARCH duration of the welding process. A and t were recorded during the experiments. Both MC and Md could be directly measured. MC is the mass difference of the core wire of the electrode before and after welding. Md is the mass increment of the 9% Ni steel plate, which could be measured by weighing the steel plate before and after welding (slag was removed before weighing). Because the mass loss during welding includes spattering, evaporating at welding temperature (in the form of welding fumes), oxidizing/ burning (in the form of oxides mixed with the slag), and residual metal particles embedded in the slag (Refs. 10, 12), the coefficient of loss, CL, was defined as CL = 1 – DR/MR (4) For quantitatively measuring the slag detachability, the images of the weld joint with the residual slag were analyzed by using the commercial Image Pro Plus software to determine the relative fraction of the slag adhesion area. Then the slag detachability rate, SDR, could be defined as SDR = A0 – As/A0 100% (5) where As and A0 indicate the slag adhesion area and the total area of the weld joint in the image, respectively. In addition, all the welding operations in this study were done by a professional welder. Some subjective judgments on the operating properties of the electrodes, such as slag fluidity and fumes, were made by the welder. The chemical compositions of the welding slag were analyzed by a Thermo Fisher ARL9900 x-ray fluorescence spectrometer (XRF). Considering that the slag was a mixture of oxides and fluoride, the analyzed result could be expressed in terms of calcium fluoride, basic oxides, and acidic oxides (Refs. 8, 9, 12, 13, 17–20). The chemical compositions of the welding slag were presented in Table 2. The basicity of each DECEMBER 2016 / WELDING JOURNAL 469-s Fig. 2 — Illustration of the weld assembly and sampling of the deposited metal. Table 2 — Compositions of Slags for the NickelBased Alloy Covered Electrodes (wt%) Type CaO CaF SiO2 TiO MnO NbO K2O NaO FeO CrO AlO MoO MgO NiO WO SrO 2 2 25 223 23 3 CaF2CaOSiO2 23.40 39.98 12.84 4.44 2.92 2.32 2.23 1.72 1.17 3.01 2.87 1.06 0.79 1.07 0.18 — TiO2SiO2SrO 3.18 17.16 13.38 23.27 5.04 1.70 3.67 8.14 0.92 2.98 7.96 0.53 1.93 1.01 0.13 9.00
Welding Journal | December 2016
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