Abstract: To precisely regulate the solidification structure of continuous casting small billets and improve billet quality, a Columnar-to-Equiaxed Transition (CET) prediction model was established. Taking SWRH82B steel as the reference material, the CET criterion constant for columnar-to-equiaxed transition was determined to be 8.93 ℃·s^1/2·mm^-3/2 under the conditions of a superheat of 27 ℃ and a casting speed of 1.6 m/min. The cooling rate was calculated by measuring the secondary dendrite arm spacing of SWRH77B steel, and the calculated values were compared with the simulated results of the model. The reliability of the mathematical model was verified, with minor errors and consistent variation trends observed. The influence laws of three key process parameters, including superheat, specific water flow rate and casting speed, on the equiaxed grain ratio were further investigated. The results indicated that the equiaxed grain ratio decreased by 1~2 percentage points with every 10 ℃ increase in superheat, decreased by approximately 2 percentage points with every 0.2 L/kg increase in specific water flow rate, and decreased by 1~2 percentage points with every 0.2 m/min rise in casting speed. The research findings provided a theoretical basis and practical guidance for the process optimization of continuous casting small billets and improvement of solidification structure.

Key words: billet continuous casting; columnar-to-equiaxed transition; solidification structure; equiaxed grain ratio