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

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 center dot Al2O3 and globular CaO-Al2O3-(MgO). Pure cluster MgO center dot 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 center dot 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.