Characterization and Thermodynamics of Al2O3-MnO-SiO2 (-MnS) Inclusion Formation in Carbon Steel Billet

A method to extract inclusion particles from solid steel by electrolysis with organic electrolyte solution was introduced; meanwhile, thermodynamics of inclusion formation was calculated using FactSage software. The results showed that there were two kinds of inclusions in the billet, i. e. Al2 O3-MnO-SiO2-MnS (AMS-MnS) and A12O3-MnO-SiO2 (AMS). Most of AMS-MnS inclusion particles, with diameter of 10 - 30 µm, showed three-layer structures: SiO2-rich core with a small quantity of Mn, intermediate AMS layer, and MnS outer layer containing small quantities of Al and O. Most AMS inclusion particles were 50 - 90 µm and exhibited homogeneous composition. Thermodynamic results indicated that SiO2-rich core could form firstly by Si reacting with O in molten steel at temperatures above 1923 K during Si-Fe alloy addition, and then, the SiO2-rich core could react with Mn and Al to form liquid AMS enveloping the SiO2-rich core at 1823 - 1873 K. MnS began to precipitate from AMS when temperature reached 1728 K. Liquid AMS could form by coupled reaction among Si, Mn, Al and O in molten steel.