Effect of Slag Compositions and Additive on Heat Transfer and Crystallization of Mold Fluxes for High-Al Non-magnetic Steel

Abstract

Intense reaction between silica in mold fluxes and aluminium in liquid steel during casting of high-Al non-magnetic steel 20Mn23AlV (1.5–2.5 Al in mass percent) would significantly alter both chemical compositions and properties of mold fluxes. This would subsequently lead to severe casting problems such as lots of slag rims, breakout and poor surface quality. Investigation carried out in this paper started with plant sampling, followed by a look at how the variation of Al₂O₃/SiO₂ ratio with reaction time can affect the casting process and product quality. Thus, this work focuses on the study of increasing Al₂O₃/SiO₂ and partial substitution of CaO with BaO in CaO–SiO₂ system mold fluxes in terms of heat transfer and crystallization behavior. The techniques implemented are heat flux simulator and single hot thermocouple technique (SHTT). The results showed that an increase in Al₂O₃/SiO₂ inhibits heat transfer, increases crystallization temperature and critical cooling rate while shortens incubation time, additionally, accelerates precipitation of phase with high melting temperature. However, greater substitution of CaO with BaO accelerates heat transfer, reduces crystallization temperature and critical cooling rate at the cost of longer incubation time even at elevated Al₂O₃/SiO₂. Eventually, partial substitution of CaO with BaO, to some extent, counteracts the effect of increasing Al₂O₃/SiO₂ on heat transfer and crystallization properties of mold fluxes for casting of high-Al steels.