Calculation and experimental study of reactivity between CaO–BaO–Al 2 O 3 –CaF 2 –Li 2 O mould slag and low density and high strength steel

Abstract

In the continuous casting of low-density and high-strength steel, minimising or eliminating steel–slag reactions is imperative to ensure stable slag properties and a smooth casting process. This study conducted steel–slag contact experiments at 1400 °C, based on thermodynamic calculations predicting the reaction trends of the proposed CaO–BaO–Al₂O₃–CaF₂–Li₂O mould slag with low-density and high-strength steel containing 8 wt-% Al. The changes in compositions, rheological, and solidification characteristics of slags pre- and post-reaction are analysed. The findings reveal that only Li₂O reacts with Al in the steel, forming LiAlO₂ rather than Al₂O₃. Reactivity is affected by component activity and the partial pressure of Li vapour at the reaction interface, established to vary between 0.154 and 0.253 atm. Within the current range of slag composition, increasing Al₂O₃ and reducing Li₂O content in the slag inhibits the slag–metal reaction. Specifically, Li₂O remains unreactive with Al when 2.5 wt-% < Li₂O  <  5 wt-% and Al₂O₃  >  27 wt-%. Conversely, the reaction occurs when Li₂O  >  4.5 wt-% and Al₂O₃ < 18 wt-%. In conclusion, low- and non-reactive mould slags suitable for casting low-density and high-strength steel are proposed, considering both reactivity and stable slag properties.