Effect of steel strip feeding on the columnar-equiaxed solidification in a large continuous casting round bloom

Abstract

The steel strip feeding process can effectively improve the macrosegregation, central porosity, shrinkage, cracking, and other defects of continuous casting (CC) round blooms. Based on the volume-averaged method, a three-phase mix columnar-equiaxed solidification model is established, which considers the nucleation, growth of the columnar and equiaxed crystals, deposition of equiaxed crystals, and transmission of solutes. The effect of the feeding strip on the temperature, velocity, phase distribution, and macrosegregation distribution in a large vertical CC round bloom was studied. The results show that the CC bloom shell is built by columnar crystals, and equiaxed crystals fabricate the central zone. The feeding of the steel strip enhanced the flow inside the liquid core, which changed the flow direction of the center and end of the liquid core. The liquid phase and the temperature field display a similar distribution, and the liquid core and V-shaped high-temperature zone will gradually shorten with the increasing feeding ratio. A highly consistent distribution of the phase and the macrosegregation was found, and the increase in feeding ratio promotes columnar-to-equiaxed transformation (CET) and improves macrosegregation. Compared with no feeding strip, the extreme values of the macrosegregation index of 1.0% feeding ratio decreased by 37.1%, and the CET point at the sectional radius increased by 17.39%.