Calculation and experimental study of reactivity between CaO–BaO–Al2O3–CaF2–Li2O 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.