ALUMINA INCLUSION BEHAVIOR DURING STEEL DEOXIDATION

A computational model based on classic homogenous nucleation theory, thermodynamic analysis and numerical simulation, has been developed to study steel deoxidation by aluminum in a low carbon aluminum-killed steel ladle, which calculates the nucleation and time evolution of the alumina inclusion size distribution due to Ostwald ripening, Brownian collision and turbulent collision. Starting with rapid supersaturation with Al2O3 “pseudo-molecules”, homogeneous nucleation is very fast, occurring mainly between 1µs and 10µs. The stable inclusion nuclei are predicted to be only about 10-20 Å in diameter. The growth of inclusions smaller than 1µm in radii, is mainly controlled by diffusion of pseudo-molecules and Brownian collision, and inclusions in this range tend to be spherical. The growth of inclusions larger than 2µm in radii is mainly controlled by turbulent collisions, and inclusions in this range tend to form clusters which retain minimum feature sizes of 1~2µm. Inclusion size distribution can reach 0.1~1µm at 6s and 0.1~36µm at 100s. Stirring powder has significant effect on the inclusion size distribution, it is recommended that first stir vigorously to encourage the collision of small inclusions into large ones, followed by a “final stir” that slowly recirculates the steel to facilitate their removal into the slag while minimizing the generation of more large inclusions via collisions