Mechanism of Desulfurization from Liquid Iron by Hydrogen Plasma Arc Melting
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urity iron has become an area of interest due to its excellent properties, such as good soft magnetism, electro-conductivity, and corrosion resistance. It is a promising component in optoelectronic semiconductor material and hard magnetic films.[1] It is well known that the properties of iron can be deteriorated significantly by sulfur, because sulfur decreases its ductility and corrosion resistance.[2] To ensure the persistence of the desirable properties noted above, sulfur content in iron should be very low. Recently, several desulfurization techniques in metallurgical processes have been explored, such as argon gas bubbling,[3–5] desulfurization slag,[6–8] and the use of desulfurization agents (Na2CO3, CaO, CaC2, and Mg).[9–15] In the argon-bubbling furnace, the efficiency of removing sulfides by bubbles and slag–metal reactions was improved.[6] Regarding the adding of Mg
XILIANG GUO, JIANBO YU, YUJIA ZHANG, XIA LI, JIANG WANG, and ZHONGMING REN are with the State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai, 200072, P.R. China and also with the School of Material Science and Engineering, Shanghai University, Shanghai, 200072, P.R. China. Contact e-mails: [email protected]; [email protected] HANLIN LIAO is with the ICB UMR 6303, CNRS, Univ. Bourgogne FrancheComte´, UTBM, 90010, Belfort, France. Manuscript submitted December 19, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
desulfurization, the magnesium sulfide inclusions were also eliminated by rising magnesium bubbles.[9] Nevertheless, the above methods did not satisfy environmental requirements, nor did they enhance the efficiency of deep desulfurization. In addition, Yang et al.[16–18] investigated the desulfurization of molten iron systematically with magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide and found that the sulfur content was reduced from 500 to 10 ppm using N2 carrier gas. However, the liquid iron was polluted with the desulfurization product alumina and nitrides introduced by carrier N2 gas. Additionally, electron beam melting (EBM) was used to refine high-purity metals.[19,20] However, there are many technical difficulties in maintaining a high vacuum condition. The considerable loss of molten metal by evaporation is also a disadvantage of purifying iron by EBM. As a practical melting method, plasma arc melting (PAM) has been widely applied in purifying various metals and alloys.[21–30] PAM can be easily accomplished at roughly atmospheric pressure. In plasma metallurgy, argon is applied for stabilizing the arc discharges and as a transfer medium for heating the materials. In such a case, the excellent refining effect cannot be expected. Fortunately, it has been determined that adding hydrogen in plasma gas accelerates the removal of non-metallic impurities such as oxygen and nitrogen from Fe and Co.[21] Many works about the removal of metallic impurities from the liquid active metals such as Ti, Zr, Cr, and Hf have been carried out with good results.[22,29–31] Kyojiro conducted the desulfurizatio
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