ON THE RELEVANCE OF MICROSEGREGATION MODELS FOR PROCESS CONTROL IN CONTINUOUS CASTING OF STEEL

Microsegregation in general is the consequence of the different solubility of alloying and residual elements in liquid and solid steel. The result is an enrichment of segregating elements between the dendrites due to incomplete diffusion equalization. This enrichment favours the precipitation of inclusions (e.g. MnS) during solidification as well as the formation of hot tear segregations (HTS) along primary grain boundaries. Hence, the modelling of microsegregation phenomena is an important task in order to predict the final product quality and to optimize the process parameters in continuous casting of steel. A microsegregation model based on the analytical solution proposed by Ohnaka was implemented in an in-house 1D-FV solidification simulation software. Considering equilibrium partition coefficients from FactSage (FSSte12015) non-equilibrium solidus temperatures of various steel grades were calculated. These results show very good correspondence with values determined from an in-situ hot tensile on solidifying steel. Finally, the results were applied to calculate solidification in a continuous slab casting machine and to analyse the strain in the mushy zone subsequently. For selected steel grades the probability of HTS formation was predicted and the influence of operating parameters was quantified.