Abstract
A major objective of calcium treatment in steelmaking is to improve product performance through inclusion modification. In order to establish inclusion modification, shape and composition of inclusions were monitored using SEM during and after addition of calcium wire into 2kg heats of steel under the various conditions of Ca consumption, Ca addition pattern and flux composition. From experimental studies of calcium treatment, the mechanism of modification of calcium aluminate and formation of CaS and MgO in inclusions was discussed from the thermodynamic point of view. The results obtained are summarized as follows.
(1) Calcium addition pattern affected composition variation of inclusions, although it had no effects on relation between [Ca] and (%CaO) in inclusions. Apparent equilibrium constant log (Kcao) was approximated to be -6.4 by thermodynamic calculation.
(2) CaS in inclusions were observed under the conditions of high Ca consumption, high [S] and low (SiO2) in flux.
(3) [Mg], increased by reduction of MgO in flux or crucible after Ca addition, reacted with calcium aluminate and formed MgO in inclusions. Critical condition for formation of MgO was represented with relation between [Ca] and [Mg].
