Abstract: A mathematical simulation was conducted using the ProCAST software for the solidification process of the large round billets. The effect of liquid steel superheat in tundish, casting speed and secondary cooling intensity on solidification of continuous casting billet were studied. The results showed that under the condition of mold electromagnetic stirring (EMES) with 300 A current and 3 Hz frequency, the equiaxial crystal ratio of casting billet increased significantly with the reduce of the degree of superheat, from 49 ℃ to 29 ℃, and the equiaxial crystal ratio increases by 4 % roughly for every 10 ℃ drop in the superheat. The equiaxial crystal ratio of casting billet increased insignificantly when casting speed increased for every 0.02 m/min up from 0.16 m/min to 0.20 m/min and secondary cooling intensity reduced for every 0.5 times from 1.5 times to 0.5 times of the standard water flow rate, only roughly 1.5 %. The grain sizes of solidification structures were refined significantly with decrease in superheat, but the changes of the casting speed and secondary cooling intensity had little effects on it. So reducing the superheat of the steel in tundish is the most effective way to improve the equiaxial crystal ratio and refine the grain size of continuous casting billet among the continuous casting process parameters.

Key words: 35 steel, large round billet, solidification structure, ProCAST, mathematical simulation