The aim of this work is to examine microstructure formation during the solidification of unidirectional solidified AISI 304 stainless steel. Numerical and experimental results indicate that this numerical model allows a precise analysis of the AISI 304 stainless steel microstructure formation. This model determines temperature profiles, position of liquid and solid isotherms, thermal parameters (thermal gradients, tip rate movement, rate cooling), and finally, the secondary inter dendritic spacing. This model was tested by comparing the experimental values results, and thus a reasonable correlation was found.