Investigation on the Origin of Al2O3-Rich Inclusions in Valve Spring Steel under Vacuum Condition

摘要

Hard and non-deformable Al2O3-rich (>70 mass%) inclusions are extremely detrimental for valve spring wire. In order to explore the origin of Al2O3-rich inclusions and provide solutions, an investigation on the effects of Al-containing MgO-C refractory and refining slag on the generation of Al2O3-rich inclusions in valve spring steel deoxidized by Si and Mn under different vacuum conditions is carried out on a laboratorial scale by a cold crucible levitation melting (CCLM) furnace. The experimental results indicate that the refractory/steel interaction under vacuum conditions has a far more significant contribution to the increase of [Al](S) (Acid-soluble Al) content in steel compared with slag/steel interaction, which further leads to the generation of Al2O3-rich inclusions. Based on the experimental results and thermodynamic calculations, the mechanisms of refractory/steel interaction and slag/steel interaction under vacuum conditions are deduced to provide a reference for the control of Al2O3-rich inclusions in valve spring steel deoxidized by Si and Mn.