Reaction Between High Mn-High Al Steel and CaO-SiO $$_2$$ 2 -Type Molten Mold Flux:
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te of Industrial Technology, Kimje, Jeonbuk 54325, Republic of Korea. MIN-SEOK PARK and SUNG-HOON JUNG are with the Technical Research Laboratories, POSCO, Kwangyang, Jeonnam 57807, Republic of Korea. SEONG-YEON KIM is with the Technical Research Laboratories, POSCO, Pohang, Kyungbuk 37859, Republic of Korea. YOUN-BAE KANG is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 37673, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted March 25, 2020, accepted September 6, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
INTRODUCTION
HIGH Mn-high Al steel has been developed as a new lightweight steel grade with extraordinary strength and ductility.[1–3] Many investigations have been carried out on its superior performance, and readers are referred to read the excellent reviews.[4,5] On the other hand, despite its attractive properties, mass production of this steel grade is still far from a commercial level. Due to the high Al content in the steel, continuous casting of this steel is very difficult when conventional CaO-SiO2 -type mold fluxes were used.[6–11] SiO2 in the flux is easily reduced by Al. This leads to a rapid increase of Al2 O3 content in the mold flux, causing a gradual change of viscosity, melting temperature, crystallization character, etc. This rapid Al2 O3 accumulation in the mold flux is
detrimental to the mold flux performances, including lubrication and heat transfer in a casting mold,[6,7] and finally causes surface crack of a cast slab, even a breakout during the casting practice. The present authors have investigated the reaction mechanism between high Mn-high Al steel and CaO-SiO2 -type molten mold flux in order to understand Al2 O3 accumulation phenomena and to control the reaction rate for better casting performance.[12–16] It was found that a major reaction causing the rapid Al2 O3 accumulation is[12,14]: 4Al þ 3ðSiO2 Þ ¼ 3Si þ 2ðAl2 O3 Þ
½1
Other side reactions involving MnO, Fet O and Na2 O were also identified.[12] In particular, reduction of additive flux components such as B2 O3 by Al was reported.[16] It should be stressed that reduction of the additive flux components by Al results in losing its intended function to perform in the flux. Reduction of B2 O3 by Al was also reported elsewhere.[17] Interested readers are also recommended to read a number of review articles discussing the recent progress in the development of the mold flux.[8–10] When the initial Al content in the liquid steel ð½pct Al0 ) was < 1.8, the overall reaction rate was controlled by mass transport of Al in the steel,[13] where the overall reaction refers to not only Reaction [1] but also other side reactions. By analyzing the measured experimental data,[12] the mass transport coefficient of Al in liquid steel was obtained[13]: ln km Al ¼
14290 1:1107 T
aluminate (MgAl2 O4 ) crystallized along with minor calcium aluminate (CaAl4 O7 ).[13,14] Due to their different shapes, the effect of each aluminate on the mass transport in the flux may be di
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