Effect of Acid-Soluble Aluminum on the Evolution of Non-metallic Inclusions in Spring Steel

Abstract

The content of acidic soluble aluminum in molten steel ([Al]s) is of significance to the control of total oxygen (TO), the formation of non-metallic inclusions, and the improvement of the surface quality of billets. Industrial trials and thermodynamic calculations were performed to study the effects of [Al]s content on the TO and the evolution of non-metallic inclusions in 60Si2Mn-Cr spring steel that was deoxidized by Si-Mn ((low aluminum process (LAP)) and Si-Mn-Al (high aluminum process (HAP)). The results show that the [Al]s contents in billets are within 0.0060 to 0.0069 mass pct in the LAP and 0.016 to 0.055 mass pct in the HAP. The TO content at each station of the LAP is higher than that in the HAP; the inclusions of billets were mainly of the CaO-Al2O3-SiO2 type in the former, and of the CaO-Al2O3-MgO and CaS-Al2O3-MgO types in the latter. A tendency is found that the higher the [Al]s, the easier it is to deviate from the low melting point region of the inclusion distribution and the larger the size of the inclusions. The relationships between [Al]s and the melting point of the oxide inclusions and the Al2O3 content in the oxide inclusions are also discussed in terms of experiment and calculation.