Influence of Calcium-treatment on Sulfide- and Oxide-inclusions in Continuous-cast Slab of Clean Steel—Dendrite Structure and Inclusions

A model proposed in another publication1) for steady state uni-directional solidification is evolved to a relationship between solidification variables and dendrite structure/morphology in non-steady state directional solidification. Dendrite structure and inclusion behaviors in columnar zone of continuous cast slabs are discussed with the model. Behaviors of inclusions in calcium-treated clean steels are discussed based on equilibrium considerations as well as widely accepted results and knowledges hitherto. An idea is introduced to interpret competitive precipitations of oxides and sulfides for calcium in residual melts between dendrite arms where the inclusions precipitate. Quantitative predictions are enabled with the present model, and several equations are given to volume fraction, size and morphology of the inclusions in calcium-treated clean steels in relation with Ca-S-O balance and solidification variables.