Inclusion modification by calcium treatment

Abstract

A major objective of calcium treatment in steelmaking is to improve product performance through inclusion modification. 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 various conditions of Ca consumption and Ca addition pattern. A mathematical model of the kinetics considering the evaporation of calcium and the reaction between inclusions and melt was developed to thoroughly examine these phenomena in calcium treatment. The calculated results were compared with the observed ones which were obtained in experiments. (1) Shape and composition of inclusions changed from a spherical SiO2-MnO system to almost lumpy Al2O3 with the addition of aluminum, and to spherical CaO-Al2O3 including CaS after addition of CaSi. (2) The process and consumption of calcium were found to affect the change of CaO and CaS contents of inclusions. (3) A mathematical model was developed assuming that vaporization rate of calcium from the melt and rate of reaction between melt and inclusions can be described by equations of the first order reaction, and that the size and number of inclusions remain constant during treatment. (4) The calculated [Ca] and CaO, CaS contents of inclusions showed good agreement with observed ones regardless of the conditions of CaSi addition. © 1996 ISIJ.