Sensitivity of Midway and Surface Crack During Solidification End Reduction on Large Sized Continuously Cast Round Bloom

In order to investigate the crack sensitivity of a continuously cast round bloom with the diameter of 690 mm during solidification end reduction, a three-dimensional finite element model coupled heat transfer and deformation was numerically developed, and it was experimentally verified by the surface temperature, shell growth and bulge amount from the plant test. It is compared that the difference between modeling and measurement in temperature is less than 15 °C, while that in shell thickness is smaller than 3 mm and in the lateral bulge amount is lower than 0.5 mm. The tensile stress and strain were observed in both surface layer and brittle zone near solidification front when the reduction is conducted before crater end, while they just concentrate on the surface if the reduction is applied after full solidification. The maximum tensile stress and strain in between liquid impenetrable temperature and zero ductility temperature in the round bloom increase monotonically as the total reduction amount increases before final solidification, and the critical reduction amount for single unit to avoid midway crack should be not higher than 15 mm according to the simulation and industrial test. The surface crack is found in the round bloom from the plant at the diagonal location when the temperature and reduction amount is not well adjusted. The critical reduction amount is about 70 mm for the casting speed of 0.26 m·min⁻¹ with the surface temperature above 800 °C by modeling, and it decreases to lower than 65 mm while the casting speed reduces to 0.24 m·min⁻¹ and surface temperature is below 800 °C according to the plant results. The reason for the high risk to midway crack in reduction on round bloom is theoretically discussed with the comparison to reported data, and the critical strain is smaller in round bloom than the rectangular. The difference in threshold reduction amount by prediction and measurement for midway crack is just about 1 mm, while for surface crack is smaller than 5 mm. It is shown that the numerical approach to evaluate the crack sensitivity is proven to be a liable method to design the reduction parameter for round bloom during continuous casting.