Morphology Control for Al2O3 Inclusion Without Ca Treatment in High-Aluminum Steel

Nozzle blockage is a major problem during continuous casting of Al-containing steel. Herein, we analyzed the thermodynamic equilibrium behavior between aluminum and oxygen in steel at 1873 K (1600 degrees C) and demonstrated that, the dissolved [O] initially decreases with increasing the dissolved [Al] until approximately 0.1 wt pct [Al], and after that, the dissolved [O] increases with dissolved [Al]. Thus, for high-aluminum steel with 1.0 wt pct dissolved [Al], the precipitation of Al2O3 inclusion can be avoided during cooling from deoxidation temperature to the liquidus temperature, if the actual dissolved [O] can be kept from increasing when the dissolved [Al] further increases from 0.1 to 1.0 wt pct. Hence, a method of inclusion control for high-aluminum steel without traditional Ca treatment technology was proposed based on the thermodynamic analysis. Industrial tests confirmed that low-melting point Ca-aluminate inclusions were observed typically through a slag washing with SiO2-minimized high-basicity slag during tapping, accompanied by two-step Al-adding process for production of high-aluminum steel. Moreover, there was no nozzle clogging occurred for five heats of continuous casting. (C) The Minerals, Metals & Materials Society and ASM International 2014