Prediction Model for Degree of Solid-shell Unevenness during Initial Solidification in the Mold

The unevenness of the solid-shell and heat flux (Phi(q)) during solidification were measured for various steel grades with casting apparatus. Then the data were used to develop a model to predict the degree of solid-shell unevenness according to the steel composition. The surface of the solid-shell was the least uniform when the steel composition was near the peritectic point, at which Phi(q) was the lowest. A model to calculate an index of solid-shell unevenness was developed under the following conditions. Solid-shell unevenness is formed at the initial solidification under the constant cooling rate, which occurs only where solid fraction (fs) is from 0.9 to 1.0. In addition, solid-shell unevenness is proportional to the amount of phase transformation and inversely proportional to the temperature range of Delta T-PT; between the temperature of fs = 0.9 and the solidus temperature. This model shows about 87% of the prediction accuracy in the experimental results of this study and also gives reasonable explanations of solid-shell unevenness observed in previous researches on steels.