The crystallisation behaviour of low melting point CaO-SiO2-Al2O3-MgO inclusions greatly affect the
deformability of inclusions during the rolling process. The crystallisation characteristics of CaO-SiO2-
Al2O3-MgO melts representing the oxide inclusions in Si-Mn killed steel were systematically
investigated. The effect of Al2O3 and MgO contents on the crystallisation change were analysed
under a fixed CaO/SiO2 in the complex inclusions. The continuous-cooling-transformation (CCT) and
time-temperature-transformation (TTT) experiments were conducted. The results showed that the
increase of MgO content increases the crystallisation ability of CaO-SiO2-Al2O3-MgO inclusions,
while the increase of Al2O3 content has the opposite effect. The viscosity, liquidus temperature of
oxide melt and also the initial crystallisation potential might be the reasons for the change in
crystallisation behaviour. Also, the crystallisation activation energy could semi-quantitatively
characterise the crystal growth during the crystallisation of inclusions. To obtain low melting point
plasticized CaO-SiO2-Al2O3-MgO (CaO/SiO2=1) system inclusions, the Al2O3 content of the system
needs to be controlled larger than 15 wt per cent and the MgO content should be kept at a small
amount.