During continuous casting of P91 steel, control of heat transfer uniformity within the mould is important to avoid surface longitudinal crack. The superior water-cooling structure helps to ensure that the shell grows uniformly within the mould, which is essential to improving the surface quality of the strand. In this study, a coupled mathematical model of fluid flow, heat transfer and thermal stress are established of Φ400 mm P91 round bloom. The accuracy of the model was verified through on-site temperature measurement experiments. A shell uniformity evaluation index (SUEI) is proposed to quantitatively characterise the uniformity of the shell, the homogeneity of the shell deteriorates as the SUEI value increases. The results of the simulation calculations indicate that a lower incidence of surface crack occurs with a water velocity of 8 m/s and a water channel diameter of 12 mm. Furthermore, the impact of altering the water channel diameter on shell uniformity exceeds that of changing the water velocity. In addition, this study quantitatively investigates the problem of thermal stress concentration due to the uneven of the solidified shell. Providing theoretical support for reducing the problem of surface crack initiation in P91 continuous cast round bloom.
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