Abstract
Kinetics analysis without fully taking into account the effect of mass transport in slag phase on MgO reduction by Al in liquid steel would lead to overestimation of Mg pickup by steel and driving force of the reaction. Two rate models considering mass transport in (a) steel melt phase only (single control model) and (b) steel and slag melt phases (mixed control model) were developed for evaluating the thermodynamic equilibria between CaO-Al2O3-MgO slags and Al-killed steels. Calculated results from the two models were compared and then validated by equilibrium experiments between a CaO-Al2O3-MgO slag (Al2O3-saturated) and Al-killed steels with different Al levels at 1873 K (1600 °C). Results showed that the calculated reaction rate in the mixed control model was always lower than that in the single control model due to the slow mass transport in the slag phase. The mass transfer coefficient of [Mg] in the steel was computed to be 6.2 × 10−5 m/s from the equilibrium experiment results between an Fe-1.0 mass% Al steel and 51 mass% CaO-39 mass% Al2O3-10 mass% MgO slag at 1873 K (1600 °C), with which the mixed control model was validated at different initial Al levels in the steels.
Highlights
Advanced High Strength Steel (AHSS) has nowadays been widely employed in the automotive industry due to its high strength, enhanced formability and lightness
MgO in the slag is probably reduced by the dissolved Al in the AHSS melt at a high temperature which leads to Mg transfer to the melt and unexpected changes to non-metallic inclusions, resulting in quality and performance problems of AHSS steel products
The correlative reaction and standard Gibbs free energy of MgO reduction by Al in liquid Fe are shown in Reaction (1) and Equation (2) [6], respectively, where “()” represents that the component is presented in the mixture of oxide melt, and “[]” represents the dissolved element in liquid Fe
Summary
Advanced High Strength Steel (AHSS) has nowadays been widely employed in the automotive industry due to its high strength, enhanced formability and lightness. The correlative reaction and standard Gibbs free energy of MgO reduction by Al in liquid Fe are shown in Reaction (1) and Equation (2) [6], respectively, where “()” represents that the component is presented in the mixture of oxide melt, and “[]” represents the dissolved element in liquid Fe. It is noteworthy that, both MgO-containing slag and refractory can be the source of Mg in Reaction 1 [7,8,9], a solid spinel layer at the steel-refractory interface probably generates and prevents direct Mg pickup by the steel which turns the MgO-containing refractory to be an inefficient source of [Mg] [10,11,12].
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