Solidification castings can exhibit a columnar or an equiaxed morphology or a combination of both. Since the relative proportions of these two components strongly influence the internal quality of cast product, the study of morphological transition from columnar to equiaxed structure (CET) becomes important. The transition also affects quality parameters like inclusion distribution in castings which has a significant bearing on the properties of cast products. In this work, a combined model for CET and inclusion distribution in continuously cast steel billets is presented. A conduction based transient thermal solidification model is employed in conjunction with Hunt's criterion for CET to predict the evolution of melt temperature, the location of transition and area-fractions of columnar and equiaxed zones across the billet cross-section. A correlation between melt temperature and equiaxed nuclei density is proposed and incorporated in the model to account for a more realistic variation of CET with melt superheat. The model is compared with available experimental data and is used to explore the effect of process parameters on CET and determine the spatial distribution of non-metallic inclusions in the solidified billet.

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