Influence of Al 2 O 3 Level in CaO-SiO 2 -MgO-Al 2 O 3 Refining Slags on Slag/Magnesia-Doloma Refractory Interactions
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NTRODUCTION
MAGNESIA-DOLOMA (or magnesia-dolomite) refractories are commonly applied in linings of stainless steelmaking units,[1–3] e.g., argon oxygen decarburization (AOD) and vacuum oxygen decarburization (VOD) ladles. This is because of the advantages of magnesia-doloma refractories, such as the low cost and their inherent stability in contact with very basic slags that are used to remove impurities such as S and P.[1,4] As a result of the worldwide adoption of magnesia-doloma refractories, a multitude of studies on the wear mechanisms of this refractory type have been reported.[5–10] Le Coq et al.[5] investigated the corrosion behavior of doloma-carbon refractories by CaO-SiO2-Al2O3-MgO-MnO-FeO-CaF2 slags (CaO/SiO2 ratio: 3.5 to 4.0, Al2O3: 28.2 to 32.0 wt pct) at 1600 C. It was concluded from their results that the main corrosion mechanisms of the refractories are the interaction between lime and slags producing calcium aluminates and calcium silicates, followed by the slag infiltration into the refractories and the dissolution of periclase grains into the slag. Similar conclusions were drawn by Jasson et al.,[7] who investigated the dissolution of doloma-based refractories in liquid CaO-Al2O3-SiO2-MgO slags with LIUGANG CHEN, ANNELIES MALFLIET, PETER TOM JONES, BART BLANPAIN, and MUXING GUO are with the Department of Materials Engineering, KU Leuven, BE-3001 Leuven, Belgium. Contact email: [email protected] Manuscript submitted November 15, 2018. Article published online May 13, 2019. 1822—VOLUME 50B, AUGUST 2019
CaO/SiO2 ratios of 4.8 to 5.2 and Al2O3 contents of 30 to 33 wt pct, at temperatures ranging from 1773 K to 1923 K. When the magnesia-doloma refractories are contacted by these CaO-SiO2–containing slags, the formation of a 2CaOÆSiO2 (C2S) layer at the slag/ refractory interface is expected.[1,6,10] The formation of such a C2S layer can retard the dissolution of refractory components into the slag and the infiltration of slag into the bulk refractory, thus mitigating the magnesia-doloma refractory corrosion. However, the formation of this protective C2S layer can be strongly influenced by the chemical composition and physical properties of the slag. It is reported by Satyoko and Lee[11] that C2S can form a discontinuous layer due to the simultaneous formation of low melting phases of magnesiowu¨stite (Fe,Mg)O and dicalcium ferrite (2CaOÆFe2O3) from the interaction between dolomite and the stagnant molten CaO-SiO2-FeO-MnO-MgO slags at 1350 C. Park et al.[6] reported that for static conditions, the thickness of the C2S layer is reduced by increasing the CaF2 content in CaO-SiO2-MgO-CaF2 slags at 1893 K, because the slag viscosity is lowered with the increase of the CaF2 level in the liquid slag. Besides the decreased slag viscosity, a high CaO solubility caused by the increased CaF2 content in the slag could also be a reason for destabilization of the formed C2S layer.[6] In stainless steel refining (e.g., AOD or VOD), CaF2 is traditionally used to increase the solubility of lime into the molten s
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