Effect of basicity on the crystallization behavior of 25 wt.%Al2O3-SiO2-CaO non-metallic inclusion-type oxides

Abstract

As a typical inclusion system in Si-Mn killed steels, the plasticity or deformability of inclusions during rolling process is significantly influenced by the crystallization behavior. The effect of basicity on the crystallization behavior of 25 wt.%Al2O3-SiO2-CaO non-metallic inclusion-type oxides was systematically investigated in the current study. A series of 25 wt.%Al2O3-SiO2-CaO system slags with different basicity were prepared to represent inclusions with corresponding compositions. The time-temperature-transformation (TTT) diagrams and continuous-cooling-transformation (CCT) diagrams were constructed introducing the single hot thermocouple technology (SHTT). The CCT and TTT tests result indicated basicity tended to promote the crystallization ability of slags, which was proved by the changes of crystallization temperature, critical cooling rate and crystallization incubation time. The maximum crystallization temperature and critical cooling rate could reach 1675.15 K (1402 °C) and 18 K/s when basicity increased to 1.55. The increase of basicity could also shorten the crystallization incubation time. The XRD results showed the precipitated crystal was gehlenite (2CaO•Al2O3•SiO2). The initial crystallization potential was proposed to reflect the crystallization ability of slags, which was calculated by FactSage, ranging from 0.317 to 1.052 with increasing basicity. Thermodynamic analysis indicated larger initial crystallization potential and lower viscosity around the melting point would be more favorable for the crystallization of melt. Under kinetic consideration, the activation energy of crystallization was calculated, decreasing from 196.511 kJ/mol to -187.649 kJ/mol when basicity increased from 1.25 to 1.55. Overall, the initial crystallization potential and crystallization activation energy could semi-quantitatively characterize the crystallization ability of slags.