Abstract: Through analyses of samples and plant data, critical steps of improving cleanliness of 20Mn2 steel were obtained, and it included control of endpoint of converter, refining process and calcium treatment. Based on integrating thermodynamics and theoretical analyses with practical process, optimized scheme including control of peroxidation at endpoint of converter by governing w(C)≥0.08%, w(P)≤0.015%, modification of refining slag by adding bauxite and adjusting amount of CaO to limit composition of slag in the range of w(CaO)=50 %－60 %, w(Al2O3)=20%－40%，w(SiO2)=5%－10%，w(MgO)=5%, and domination of reoxidation and length of CaSi wire within 145－216 m was obtained. Industrial trials of optimized scheme showed that continuous casting heats increased from 5.9 heats to 14 heats，oxygen content in steel declined dramatically, amount and dimensions of inclusions diminished.

Key words: 20Mn2 steel, cleanliness, endpoint of converter, refining process