Effect of B 2 O 3 on Crystallization Behavior, Structure, and Heat Transfer of CaO-SiO 2 -B 2 O 3 -Na 2 O-TiO 2 -Al 2 O
- PDF / 3,394,267 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 88 Downloads / 235 Views
xes are indispensable for the continuous casting of defect-free steel products, providing appropriate heat transfer control, lubrication, thermal insulation, inclusion entrapment, and oxidation prevention.[1] The amount of heat withdrawn from liquid steel during solidification is primarily dependent upon the thermo-physical properties of mold flux film. An inappropriate control of heat transfer in continuous casting process could result in a breakout of steel strand and even a halt of operation if heat transfer rate is excessively low, or longitudinal cracks caused by uneven heat distribution along solidifying steel strand surface if the heat transfer rate is too high.[2,3] Therefore,
JIAN YANG, JIANQIANG ZHANG, YASUSHI SASAKI, and OLEG OSTROVSKI are with the School of Materials Science and Engineering, University of New South Wales, Sydney, NSW, 2052, Australia. Contact e-mail: [email protected] CHEN ZHANG and DEXIANG CAI are with the Baosteel Group Corporation Research Institute, Shanghai, 201900, China. YOSHIAKI KASHIWAYA is with the Department of Energy Science and Technology, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto, 606-8501, Japan. Manuscript submitted October 13, 2016. Article published online May 18, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
understanding the heat transfer phenomenon between steel strand and copper mold is important for the prevention of the aforementioned imperfections. Mold fluxes with high crystallization tendency are typically recommended in the casting of cracking-sensitive steel. The thick crystalline layer is effective in suppressing heat removal from liquid steel in terms of its high thermal resistance. The grain boundaries of crystals scatter photons, which reduces radiative heat transfer.[4,5] Pores, cracks formed in the crystalline layer, and air gaps between the mold and the flux film also exert a high thermal resistance, which minimizes the unevenness of steel shell and, therefore, the localized thermal stresses on a solidified shell.[4–6] Currently, most of the commercial mold fluxes contain fluorides, e.g., CaF2 and NaF, to control heat transfer rate through the precipitation of cuspidine; fluorides also decrease the viscosity of mold fluxes.[7–9] However, the emission of gaseous fluorides, such as HF, SiF4, and NaF, at high temperature brings about dreadful pollution to atmosphere (acid rain), ground water (low pH-value), and health problems (brain, bone, kidney damages, etc.).[1,10–17] Taking account of the ever-rising environmental concern for steelmaking industry, the development of fluorine-free mold fluxes is of great significance. The major challenge in the development of fluorine-free mold fluxes is an effective control of heat transfer.
VOLUME 48B, AUGUST 2017—2077
Although several substitutes for cuspidine were proposed in the fluorine-free mold fluxes, such as Ca11Si4B2O22,[13–18] Ca2Si3Na2O9,[11] and CaSiTiO5,[12] the lack of fundamental knowledge of crystallization of fluorine-free flux system inhibits their application in the steelmaking industry. Ca11Si4B2O2
Data Loading...
