<p>To clarify the effect of slag/steel reaction on chemical compositions and inclusions of quenching and partitioning steel, the equilibrium experiments were carried out between 0.19C-1.7Si-2.7Mn-Al steel with two Al contents (initial content was 0.03% and 1.42%.) and 66.4wt%CaO-27.6wt%Al₂O₃-3wt%MgO-3wt%SiO₂ slag. The results showed that, after the slag/steel reaction for low Al steel, the Al content increased from 0.03 to 0.062%, and Si decreased from 1.74% to 1.64%. The content of Al₂O₃ and SiO₂ in the slag changed from 27.6 to 27.31% and 3% to 5.61%, respectively. For high Al steel, the Al decreased from 1.42% to 0.97% and Si increased from 1.73% to 1.83%. The Al₂O₃ and SiO₂ varied from 27.6% to 28.52% and 3% to 2.21%, respectively. The above trend of composition variation agreed well with the results calculated by FactSage. The main inclusions in the low Al steel were MnS before the reaction which changed to MgO after the reaction. For high Al steel, the main inclusions transformed from MnS and AlN to CaO-MgO-Al₂O₃. Thermodynamic calculations indicated that the main reducing agent was Si in the slag/steel reaction for the low Al steel, whereas it changed to Al for the high Al steel, which resulted in the differences of composition change and inclusion transformation for the steel with two Al contents.</p>