Effect of Slag Composition on the Deoxidation and Desulfurization of Inconel 718 Superalloy by ESR Type Slag Without Deo
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DUCTION
THE invention of superalloys can be tracked back to the early twentieth century.[1] Since then, Ni-based alloys, compared with Fe- or Co-based alloys, have been widely utilized in the aerospace power generation industries and other applications requiring good combinations of fatigue, oxidation and corrosion resistance and strength at elevated temperature.[2–5] However, the presence of sulfur and phosphorus, the most common impurities and detrimental elements, can deteriorate the machine properties of the superalloy.[6] Many researchers have published their results on the detrimental effects of sulfur
SHENG-CHAO DUAN, XIAO SHI, MAN-CANG ZHANG, BIN LI, WEN-SHENG YANG, HAN-JIE GUO, and JING GUO are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), 30 Xueyuan Road, Haidian District, Beijing, 100083, P.R. China, and also with the Beijing Key Laboratory of Special Melting and Preparation of HighEnd Metal Materials, University of Science and Technology Beijing (USTB), Beijing 100083, P.R. China. Contact e-mail: [email protected] FEI WANG is with the Tianjin Cisri-Harder Materials & Technology Co. Ltd., Central Iron and Steel Research Institute (CISRI), Tianjin 301721, P.R. China. Manuscript submitted May 23, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
segregation to grain boundaries in superalloys.[7–11] The sulfocarbide phase (M2SC) has been identified by Wallace et al.[7] and Whelan et al.[8] in cast and powder-fabricated nickel-based alloys, such as 713LC and IN 100 alloys. They pointed out that the M2SC particles were the crack initiation sites and crack propagation paths in the nickel-based alloy. Sun et al.[9] reported the same problem for the Inconel 718 alloy. They found that the formed needle-like (Nb,Ti)2SC can act as the nucleation site for Laves phase precipitation. The formation of a low-melting Ni-Ni3S2 eutectic film along the nickel grain boundaries can also result from the presence of sulfur, which may be responsible for the high-temperature intergranular failure.[10] In 1999, Song et al.[11] carried out studies to clarify the effect of the interaction between sulfur and phosphorus on the stress and creep properties of the Inconel 718 alloy. According to their findings, they concluded that sulfur could diminish the beneficial effect of phosphorous on the nickel-based alloy and the upper limit of sulfur should be20 pct. These observations reported in the current study can be explained by the fluoride evaporation from molten slag, causing the rest of the fluoride to have no appreciable effect on the variation of the total oxygen content.[62–64] The experimental data obtained in this work have been compared with those reported by Chen et al.[41] for experiments on deoxidation equilibrium between Inconel 718 alloy and 60 pct CaF2-20 pct CaO-20 pct Al2O3 slag under Ar gas atmosphere in a 50-kg ESR furnace. Figure 4(b) shows that there is agreement with the result reported previously by Chen et al.[41] Meanwhile, the effect of MgO content on
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