Effects of Reoxidation of Liquid Steel and Slag Composition on the Chemistry Evolution of Inclusions During Electroslag
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ODUCTION
DRAWING-INGOT-TYPE electroslag remelting (ESR) could not only significantly increase the productivity, but also enhance the product yield compared with conventional stationary type ESR. This technology has been increasingly equipped to produce special steels and alloys. This type of ESR configuration consists of a fixed mold arranged at the working platform and a retractable baseplate to draw the remelted ingot from the bottom of the mold by a frequency-controlled servo drive system during an on-going ESR process. Some dedicated slags have been developed to meet the demands of providing a stable drawing-ingot operation throughout the ESR and sound surface quality of the as-cast remelted ingot.[1,2] It has been demonstrated that the addition of SiO2 to ESR-type CaF2-CaO-Al2O3 slag is indeed effective in enhancing the stability of the
CHENGBIN SHI and JING LI are 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] HUI WANG is with the Shougang Research Institute of Technology, Beijing, 100041, P.R. China Manuscript submitted October 20, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
drawing-ingot operation during ESR and pronouncedly improving the surface quality of as-cast ingots.[1] However, the influence of varying SiO2 additions in ESR-type slag on the refining efficiency of ESR, such as the inclusion characteristics and desulfurization, has not been clarified yet. The increasing demand for more excellent performance of die steel has urged metallurgists to further improve steel cleanliness. Slag compositions exert a great influence on oxide inclusion characteristics (chemistry, number density, and removal, etc.) during conventional secondary refining of liquid steel in industrial practice.[3–7] There is no exception for ESR refining technology. ESR is very different from conventional refining technologies in terms of its practical operations and refining principles. It is quite necessary to investigate the effect of slag composition on inclusions during ESR. Allibert et al.[8] reported that slags with substantial amounts of SiO2 provided means to control the inclusion composition in remelted steel. Nevertheless, Allibert et al.[8] did not describe the inclusion compositional change related to SiO2-containing slags and its evolution mechanism. Although several studies[9,10] have focused on understanding the influence of the slag composition on inclusions during the ESR process, these previous studies did not reveal the effect of varying SiO2 contents in slag on inclusions.
Reoxidation of liquid steel is one of the major causes of the formation of oxide inclusions.[11–13] However, the inclusion formation during reoxidation of liquid steel in the ESR process has not been studied yet. In the current study, the combined effects of varying SiO2 contents in CaF2-CaO-Al2O3-MgO-SiO2 slag and the reoxidation of liquid steel during ESR on the oxide inclusion chemistry and alloying element (Si and Al) conte
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