Study on steel deoxidation with Al-Ca compound alloy

The thermodynamic diagram of calcium-aluminum-oxygen ternary system was determined through thermodynamic equilibrium calculation of liquid steel deoxidation. Based on this thermodynamic diagram and assuming 100% yield of Ca addition, the evolution mechanisms of inclusions with three different deoxidation schemes were predicted, including M kg addition of m_Ca/m_Al=5 alloy, M kg addition of m_Ca/m_Al=0.2 alloy and 0.2M kg addition of m_Ca/m_Al=0.2 alloy. The calculated results show that the evolution history of inclusion is affected by both the addition quantity and Ca/Al mass ratio of Al-Ca deoxidizer. The optimal deoxidation scheme is that the Ca/Al mass ratio is 5 and addition quantity is M kg, which makes the initial[Ca] content of 0.01% and initial[Al] content of 0.002% in liquid steel. Under such a condition, the evolution history of inclusions is 12CaO·7Al₂O₃(l)/CaO·Al₂O₃(l)→CaO(s)→12CaO·7Al₂O₃(l)/CaO·Al₂O₃(l)→CaO(s)→ 12CaO·7Al₂O₃(l)/CaO·Al₂O₃(l), and the desirable alternative formations of solid and liquid inclusions can be realized during LF refining, which can greatly enhance the effective collision and promote the floating up of inclusions. The results can be applied in industry for steel deoxidizer selection and deoxidation operation.