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.

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