Evolution of Oxide Inclusions in Si-Mn-Killed Steel During Protective Atmosphere Electroslag Remelting
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INTRODUCTION
ELECTROSLAG remelting (ESR) has superior ability to remove non-metallic inclusions from liquid metal. Like secondary refining of liquid steel (such as RH and LF refining), complete removal of oxide inclusions in liquid steel during ESR is not possible. An alternative effort is to properly control the chemistry of inclusions in order to minimize the detrimental effects of residual inclusions to the steel. Kolpishon et al.[1] reported that the chemistry of oxide inclusions was dependent on the aluminum content in high-Cr steel, and the increase in aluminum content above 0.03 pct led to AlN inclusion formation in electroslag remelted steel. Schneider et al.[2] reported that the slag with different CaO and SiO2 contents exerted a pronounced effect on the relative amounts and size distribution of MgOÆAl2O3 spinel, calcium-magnesia-aluminate, and sulfide inclusions in the remelted ingots. The present authors’ previous studies[3–5] experimentally demonstrated that the slag composition, reoxidation of liquid steel and calcium addition during ESR exerted a significant effect on the chemistry of oxide inclusions in the remelted steel.
CHENGBIN SHI is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing (USTB), Beijing 100083, P.R. China. Contact e-mail: [email protected] JOO HYUN PARK is with the Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: [email protected] Manuscript submitted December 10, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Like the oxide inclusion control during ESR process, the chemistry modification of oxide inclusions during liquid steel refining (such as LF, VD, and RH refining) for consumable steel electrode manufacturing for ESR likewise plays an important role in practice. In order to improve the steel cleanliness, different kinds of deoxidizing agents are generally employed for liquid steel deoxidation according to the requirements of individual steel grade when producing steel electrode for ESR, which consequently generates different types of inclusions in the steel electrode, such as Al2O3, MgOÆAl2O3 and various calcium aluminate inclusions. Different types of inclusions basically experience various evolution trajectories during ESR, as demonstrated in the previous studies regarding Al2O3, MgOÆAl2O3, nitride, sulfide, and calcium aluminate inclusions.[3–9] The nitride and sulfide inclusions in the consumable steel electrode were removed by dissolving as single soluble element into liquid steel during ESR process.[3,4,6–8] Shi et al.[8] found that some of CaO-Al2O3-MgO inclusions in the consumable steel electrode were transformed to liquid CaO-Al2O3-SiO2-MgO inclusions through reacting with the dissolved oxygen supplied from the reoxidation of liquid steel and concerned elements in liquid steel during ESR. Li et al.[9] reported that most of CaO-MgO-Al2O3 inclusions in steel electrode were absorbed by the molten slag during ESR, whereas limited dissolution of CaO-MgO-Al2O3 inclusions took plac
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