Study on Transformation of Glassy and Crystalline Inclusions in Cord Steel during Heat Treatment at 1100 °C

Abstract

To clarify the transformation of the glassy and crystalline inclusions in cord steel during heat treatment, four groups of MnO–SiO₂–Al₂O₃ systems with different MgO contents are designed to obtain samples with both glassy and crystalline inclusions by slow-cooling, and then the samples are isothermal held at 1100 °C for 120 min. The results of X-ray diffraction and scanning electron microscope and energy dispersive spectrometer indicate that after isothermal holding, the MgMnSiO₄ crystalline phase transforms into MgAl₂O₄ and MnSiO₃ phases in 5 wt% MgO system, while partial MgMnSiO₄ phase transforms into MgSiO₃ phase in 10 wt% MgO system. Besides, the MgMnSiO₄ crystalline phase transforms into MgSiO₃ and Mg₂SiO₄ phases in 15 wt% MgO system, while the Mg₂SiO₄ crystalline phase partially transforms into MgSiO₃ phase in 20 wt% MgO system. Combined with the calculation results of FactSage 8.1, it shows that the higher the MgO content in the system, the stronger the crystallization ability and the easier the formation of the crystalline phase. During the isothermal holding process, the elements in inclusions continuously diffuse and migrate, so that the glassy phase transforms into crystalline phase, while the crystalline phase grows further and the internal glassy phase disappear, accompanied by the transformation of the crystal type.