Characterization and evolution of non-metallic inclusions in GCr15 bearing steels during cooling and solidification

Abstract

Industrial experiments and thermodynamic calculations were performed to investigate the evolution of non-metallic inclusions during cooling and solidification of GCr15 bearing steels with different steel compositions. Non-metallic inclusions in bloom and rolled rod were characterized using the improved non-aqueous electrolysis method firstly. Inclusions in molten steel were mainly irregular MgO·Al₂O₃ and globular CaO–Al₂O₃–(MgO). Pure cluster MgO·Al₂O₃, MgO–Al₂O₃–CaS–(MnS) and MgO–Al₂O₃–(CaS)–MnS, CaO–Al₂O₃–(MgO)–CaS, MnS and cubic TiN precipitates were observed in bloom. The high-temperature heating accelerated the precipitation of MnS on the MgO·Al₂O₃ and more MgO–Al₂O₃–MnS complex inclusions were detected in rolled rod. During the continuous casting, CaO–Al₂O₃–(MgO) type inclusions in molten steel fully or partially transformed into MgO–Al₂O₃–CaS. The MgO and CaS content in inclusions increased while the CaO and Al₂O₃ content decreased during the transformation. Details of inclusion transformation were illustrated by thermodynamic calculations.