Evaporation Mechanism of Sn and SnS from Liquid Fe: Part III. Effect of C on Sn Removal
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cover an effective use of ferrous scrap as an alternative iron source instead of iron ore, much research has been carried out to develop a technology for the economic and effective use of the ferrous scrap. However, some tramp elements such as Cu, Sn, Ni, and Zn, found in ferrous scrap are known to cause contamination of the recycled steel, and the presence of those tramp elements hinders active recycling of the ferrous scrap. Among those tramp elements, Sn is found in the ferrous scrap mainly as the form of tinplate. Sn, if it enters in steel products, leads to deterioration of drawing and forming properties by a loss of ductility of steel. Therefore, the Sn content in steel is strictly controlled.[1] To minimize the undesirable aspect of Sn, various removal methods have been proposed. In particular, Sn removal by vacuum distillation has been actively investigated, thanks to the availability of vacuum facilities in most of steelmaking plants. Basically, Sn in the liquid SUNG-HOON JUNG, Graduate Student, and YOUN-BAE KANG, Associate Professor, are with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, Republic of Korea. Contact e-mail: ybkang@ postech.ac.kr JEONG-DO SEO, Senior Principal Researcher, JOONG-KIL PARK and JOO CHOI, Group Leaders, are with the Steelmaking Research Group, Technical Research Laboratories, POSCO, Pohang, Kyungbuk, 790-785, Republic of Korea. Manuscript submitted August 5, 2014. Article published online October 31, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
steel evaporates to gas phase due to the difference in the vapor pressures of Fe and Sn. Previous research for the Sn evaporation mainly focused on (1) the Sn evaporation reaction mechanism and (2) maximizing the evaporation rate of Sn. It was revealed that S could enhance the evaporation rate of Sn significantly, and the degree of vacuum is also a key factor to increase the evaporation rate.[2–8] Also, the effect of alloying elements on Sn evaporation rate has been investigated.[7–13] Although it has been understood that Sn can evaporate from liquid steel in the form of SnS(g) gas species, only a qualitative interpretation was available in the literature. The evaporation rate of Sn could not be well represented. In the present authors’ previous study, it was elucidated for the first time that S plays two opposite roles for the evaporation of Sn from the liquid steel: (1) S enhances the evaporation of Sn by forming SnS(g) gas species, which has significantly higher vapor pressure than Sn(g), and (2) S retards the evaporation of Sn by blocking the reaction sites, both for Sn(g) and SnS(g).[14,15] It was also found that there are residual sites for the evaporation that could not be blocked by the S.[15] Taking into account all these facts, a comprehensive evaporation model for the Sn in Fe-S-Sn alloy was developed, and it has been validated by the present authors’ own experiment for alloys having 0 to 0.894 mass pct of S content at 1873 K (1600 C).[15] In the actual scrap r
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