Study on formation of dual-phase MnO–SiO2-based inclusions in tire cord steel

Abstract

In order to understand the formation of dual-phase MnO–SiO2-based inclusions in tire cord steel, laboratory and industrial experiments are carried out to investigate the formation and evolution of inclusions during Si–Mn deoxidation, and thermodynamic calculations are conducted to check the stability of inclusions after deoxidation. The results show that (Fe, Mn)O inclusions and CaO–SiO2–FeO based inclusions are mainly found in BOF as-tapped crude steel. During Si–Mn deoxidation, the (Fe, Mn)O inclusions will transform into MnO–SiO2 system inclusions, including liquid MnO–SiO2 inclusions and SiO2 + MnO–SiO2 dual-phase inclusions; while CaO–SiO2–MnO inclusions will be generated from CaO–SiO2–FeO based inclusions. In Si–Mn-killed tire cord steel, SiO2 is proved to be saturated in the MnO–SiO2 system inclusions, thus the dual-phase inclusions of SiO2 + MnO–SiO2 can stably stay in liquid steel after deoxidation, and probably change into dual-phase MnO–SiO2–Al2O3 system inclusions during refining process. The effect of alloy addition sequence on deoxidation is not evident, while the effect of slag is more profound. Proper addition of slag formers should be considered to promote deoxidation result.