During continuous casting process (CCP), liquid steel is cast from the tundish to a mold. Here the steel adopts the mold section geometry (squared section) and begins to be quenched using a primary cooling system incorporated in the mold walls. Then steel billets are quenched using a secondary cooling system. Finally the steel billets are driven along a free zone to be cut and stored as a new product. During this industrial process, different grain structures are formed as a function of the heat removal conditions and the corresponding solidification speed. Near the billet surfaces a chill zone is initially formed followed by a columnar grain zone and finally an equiaxed zone in the core. A computational simulator based on stochastic methods and cellular automaton (chaos theory) is described in this work. The algorithms and equations used are also explained in detail. Computational arrays of the heat removal process previously calculated are saved and reloaded to assign solidification times and rebuild the billet thermal history [5]. The simulator includes computational algorithms for grain nucleation and grain growth in every zone. Routines for pre-nucleation and pre-growth have been also added for an improved simulation and a graphical user interface was used to display on the screen the structures simulated.