Degradation mechanism of MgO–MgAl2O4 dual-phase refractory in contact with the automobile gear steel SCr420H with Si–Mn, Al and Ce–Al deoxidation

Abstract

The current research, the degradation mechanism of MgO–MgAl2O4 dual-phase crucibles in contact with steel SCr420H with Si–Mn, Al, and Ce–Al deoxidation was investigated using a laboratory steelmaking experiment at 1873 K. The refractory interface in contact with the steel and inclusions was analysed using SEM and EPMA. In the case of Si–Mn deoxidation, the refractory's MgO phase was initially attacked by the dissolved Si, resulting in its transformation into the 2MgO–SiO2 phase, as confirmed by thermodynamic calculations. In the case of Al deoxidation, the reaction between the dissolved Al and the refractory had a significant effect on the increase in Mg concentration and MgAl2O4 inclusions. Refractory degradation was suppressed because the MgAl2O4 phase was an equilibrium phase based on thermodynamic consideration. The distribution of the MgAl2O4 phase in the refractory hindered the degradation reaction. The primary degradation mechanism in the case of Al deoxidation was steel penetration. In Ce–Al deoxidation, both Ce and Al were involved in refractory degradation. During this process, the MgO phase reacted with the dissolved Al, leading to its transformation into the MgAl2O4 phase, which was subsequently modified to the Ce–Al–O phase. Additionally, the MgAl2O4 phase was directly denatured into the Ce–Al–O phase.