Effect of Refractory on Nonmetallic Inclusions in Si-Mn-Killed Steel

Some laboratory experiments are carried out to study the effect of different refractories on the original and exogenous inclusions in Si-Mn-killed steel. As expected, it is found that Al2O3 refractory causes high melting points of both SiO2-Al2O3-MnO system and SiO2-Al2O3-CaO system inclusions, while MgO crucible reduces the melting points of both systems of inclusions to a certain extent. The purity of MgO refractory is crucial for tire cord steel grades, and even 0.3% of Al2O3 impurity in refractory results in an evident increase (by 10%-20%) of Al2O3 content in the inclusions. Similar to Al-killed steel grades, MgO center dot Al2O3 spinel can also be stable in Si-Mn-killed steel due to the effect of MgO refractory, and MgO and Al2O3 inclusions can transform into MgO center dot Al2O3 spinel. These inclusions should be strictly controlled during refining process. High-purity and high-quality MgO refractory as well as high-quality alloys are recommended for Si-Mn-killed steel grades, and Al2O3-based refractory should be avoided.