Heavy reduction (HR) is an effective technique to control V segregation in continuous casting bloom, but the effect of segregation improvement is limited by the parameters such as reduction position and reduction amounts. In order to improve the macrosegregation of bloom, numerical simulation and plant experiments are adopted in this research. A heat transfer model and a reduction model with comprehensive thermo-physical parameters were established. The two models were verified by comparing the measured surface temperature and the theoretical strain at the solidification front. It is determined that the position of the HR of the bearing steel bloom is 20.82 m~24.97 m from the meniscus, and the solid fraction in the center of the bloom is 0.6~1. The total reduction of the HR is set to 30 mm, and the reduction of each roller in the reduction range is set to 4 mm, 5 mm, 9 mm, 7 mm, and 5 mm, respectively, to prevent the formation of internal cracks. Plant trials were conducted to verify the effect of the optimized HR. The results show that the carbon segregation degree on the V channel and non-channel of the bloom decreases from 1.2 to 1.16 and increases from 0.93 to 0.95, respectively, and the central carbon segregation degree decreases from 1.17 to 1.15. Meanwhile, the internal crack was not found in the bloom.

The heat transfer calculation and the modal analysis of a 0.15 m × 0.15 m continuously-cast billet were carried out in this study. At the position of 44% linear liquid phase ratio, the results show that only for the first and sixth order modes, the displacement amplitude is in the same direction as the inner and outer arcs. Based on the first-order mode, impact vibrations are applied to the outer arc of the billet, and the impact vibrations do not damage the billet when the impact velocity v ≤ 12 m/s or the impact acceleration a ≤ 800 m/s 2 . It was found that the response of the stress on the shell was in the form of an "n-shaped" distribution under different condition vibrations. Meanwhile, it has been confirmed by experiments that large impact kinetic energy and impact momentum can improve central segregation and shrinkage porosity, respectively.

Based on the thermal-mechanical coupling model, the distance from the critical position of the shrinkage cavity formation of the two bearing steel blooms to the meniscus is 22 and 19.78 m, respectively, and the critical center solid fraction is 0.7145 and 0.7033, respectively. Furthermore, the effects of superheat and casting speed on the critical value of shrinkage cavity formation are discussed. The results show that the two factors have a great influence on the critical position of shrinkage cavity formation in the former, but basically do not affect the critical solid fraction of shrinkage cavity formation. Finally, the industrial heavy reduction tests in different reduction intervals were carried out, and the results show that when the initial reduction position of the heavy reduction process is set before the critical solid fraction, it can not only eliminate the central shrinkage cavity of the bloom, but also improve the central segregation.

Application of vibration impact at the outer arc side of a billet with a central linear liquid fraction of 25% -35% at 9.5 m from the meniscus. The results show that the impact vibration with low frequency and high impact energy can not only reduce the central porosity degree of the billet from 1.532 to 1.169, but also compact the liquid core, improve the central porosity and promote the heterogeneous nucleation of the molten pool. High frequency and low impact energy can not only increase the proportion of mixed crystal zone by about 8 %, but also reduce the central carbon segregation index from 1.08 to 1.04. Meanwhile, the two kinds of impact vibrations increase the area ratio of the central carbon segregation index in the range of 0.95-1.05 from 56.32% to 70.26% and 80.17%, respectively, and uniform the central carbon distribution of the billet.