Evaporation Mechanism of Cu from Liquid Fe Containing C and S
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STEEL is one of sustainable materials, because it is produced with reasonably cheap cost and it is also highly recyclable. Moreover, because of the limitation of sound iron ore and demand for lowering CO2 gas emission generated from blast furnace and oxygen steelmaking process, ferrous scrap consumption has been increasing. However, Cu is typically introduced in the ferrous scrap collected from electric motors. It causes hot shortness and surface defect by segregation along grain boundary and surface during hot rolling process in the temperature range of 1373 K to 1573 K (1100 C to 1300 C). Therefore, Cu content in steel is strictly restricted below 0.2 mass pct. Furthermore, oxygen affinity of Cu is weaker than that of Fe, it prevents the dissolved Cu in liquid steel from being removed by conventional oxidation refining process. Accordingly, Cu removal has become one of the serious problems against the active use of ferrous scrap, and the situation would become worse until reliable Cu removal process is developed. SUNG-HOON JUNG, formerly Graduate Student with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, Republic of Korea, is now Senior Researcher with the Gwangyang Process Research Group, Technical Research Laboratories, POSCO, Kwangyang, Cheonnam, 545-878, Republic of Korea. YOUN-BAE KANG, Associate Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted November 9, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
This problem has been already recognized, and a number of processes have been proposed for Cu removal: vacuum distillation,[1–10] sulfide flux refining,[11–18] low-melting point bath,[19] and chlorination.[20–25] However, some of the approaches showed relatively low-refining efficiency as well as some inherent disadvantages of the processes. Among those approaches, Cu removal from liquid steel by evaporation[1–10] has been one of active research topics, because the evaporation of Cu has advantages of (1) additional slag or flux are neither required nor generated, and (2) possibility of use of existing steelmaking plant facilities, for instance, vacuum degassing vessels, with a minimal modification. Main concept of this method is removing Cu as gaseous form, utilizing differences of the vapor pressure of Fe and that of Cu. Previously, researchers studied reaction kinetics of Cu evaporation in order to clarify rate determining step.[1,3–5,8–10] Also, effect of C or Si on the evaporation kinetic and thermodynamics has been conducted.[4,7,11] Hidani et al.[6] reported that Cu evaporation rate was accelerated by blowing NH3 gas onto the surface of liquid steel containing Cu. The evaporation reaction kinetics of Cu from liquid Fe-Cu alloys[1,4–7,10,11] and Fe-C-Cu alloys[1,5,7,10] was relatively well investigated in previous investigations. However, it was observed in some of previous investigations[2,4,8] that Cu evaporation co
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