An analytical model of macro-micro type for predicting the microstructure of continuous cast steel is presented in this paper. The macroscopic part is based on a finite element model to solve the nonlinear heat conduction equation. The microscopic part consists of a solute diffusion model to predict undercooling, followed by a dendrite growth model to predict columnar dendritic features. The geometry of the model corresponds to an I-shaped steel beam blank that is continuously cast to near-net shape. Good agreement is found between the predicted and the measured secondary dendrite arm spacing in an actual continuous cast I-shaped steel beam blank.