Abstract: The model of the heat transfer and solidification in the 165 mm×225 mm Q235B steel rectangular billet continuous casting process was carried out by coupling solidification shrinkage, bulging deformation, air gap, slag and mold flux heat transfer. And this model was used to calculate heat transfer and solidification of molten steel in the mold with 1.5 m/min casting speed. The results show that the wide surface temperature distribution of continuous casting billet is uneven under the influence of air gap distribution, and the formation of vibration marks can be divided into four stages compared with the shell. The first stage occurs within 0-0.17 m from the meniscus. The normal direction of the high temperature distribution is perpendicular to the direction of casting, and the vibration marks which normal direction is perpendicular to the direction of casting are formed. The second stage occurs within 0.17-0.26 m from the meniscus, the temperature distribution presents W-shape, and the vibration marks which are parallel to the casting direction are formed. The third stage occurs within 0.26-0.36 m from the meniscus, the temperature in the width direction is further homogenized, and the vibration marks parallel to the casting direction are also further homogenized. The fourth stage occurs within 0.36～0.80 m from the meniscus. The temperature distribution along the width direction of slab tends to be stable and the vibration mark also tends to be stable. The vibration marks morphology of the breakout billet is similar to the calculated temperature distribution. The calculation model can be used to explain the heat transfer and solidification behavior of continuous casting billet under this condition. After increasing the taper of the mold and adjusting the rigidity of the mold, the breakout ratio, the bulging ratio and the ratio of out-of-square exceeding the standard decrease significantly.

Key words: solidification shrinkage, bulging, air gap, heat transfer, continuous casting, mold