Study on the Equilibrium Between Liquid Iron and Calcium Vapor
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DUCTION
AN important focus for the steel industry in order to improve material properties and decrease problems during processing is control of the population of non-metallic inclusions. Calcium addition in the ladle, referred to as calcium treatment, is a common method for modification of alumina-containing inclusions into liquid calcium aluminate inclusions. The possibility of modification of inclusions via the top slag has also been discussed. Due to the high vapor pressure of liquid calcium at steelmaking temperatures as well as the very low solubility of calcium in liquid steel, it is challenging to perform calcium treatment in an efficient and, with respect to different heats, consistent manner. In order to achieve this, knowledge of the thermodynamic properties of calcium dissolved in steel at steelmaking temperatures is essential to appropriately describe the reactions involving calcium taking place between steel and slag and steel and non-metallic inclusions. Several researchers have studied the iron-rich side of the iron-calcium system at temperatures in the range of 1823 K to 1880 K (1550 °C to 1607 °C) using different experimental techniques.[1–4] Due to the high vapor pressure of calcium in the temperature range of interest and the stability of calcium oxide, the studies have been performed in closed or pressurized systems. In order to determine the activity coefficient of calcium in liquid iron, Song and Han[1] studied the solubility of calcium in liquid iron in equilibrium with varying calcium vapor pressures at 1873 K (1600 °C), while Fujiwara et al.[2] studied the partitioning of calcium between liquid iron and liquid silver at 1823 K (1550 °C). Ko¨hler et al.[3] and Sponseller and Flinn[4] studied the solubility of calcium MARTIN BERG and DU SICHEN are with the Department of Materials Science and Engineering, Royal Institute of Technology, Brinellvgen 23, SE-100 44 Stockholm, Sweden. Contact e-mail: [email protected] JAEWOO LEE is with Hyundai Steel, 1480 Bukbusaneop-ro, Songak-Eup, Dangjin-Si, Chungnam, 31719, Korea. Manuscript submitted November 1, 2016. Article published online February 27, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B
in liquid iron in contact with liquid calcium at 1873 K and 1880 K (1600 °C and 1607 °C) in pressurized systems. While the previous studies cover a relatively wide composition range, viz. 0.3 to 320 ppm by weight, there are some disagreements and scatter in the data, especially at lower calcium contents. The aim of the present study is to provide additional data on the solubility of calcium in liquid iron under varying calcium potentials at steelmaking temperatures.
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EXPERIMENTAL
Experimental measurements were made in order to study the dissolved calcium content in iron after equilibration with calcium vapor. The principle of the experiments was to equilibrate iron and calcium held at different temperatures in a closed container. By varying the temperature of the calcium, and thus the vapor pressure of calcium in the container, the iron was subjected to different calc
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