Effect of Nozzle Injection Mode on Initial Transfer Behavior of Round Bloom

Abstract

A coupled three-dimensional numerical model combining fluid flow, heat transfer, and solidification has been established to study the effect of two types of nozzle on the internal quality of LZ50 steel in a φ 690 mm sized continuously cast round bloom. The model is validated by measured data of the strand surface temperature for plant tests. According to the simulation and experimental results, it is found that the larger tangential velocity on meniscus and the higher vortex depth in the six-port nozzle is beneficial to melting mold powder and the floating removal of inclusions. When the injection mode is the six-port nozzle, the level fluctuation was an effective control to avoid slag entrapment, and the washing effect with multiple swirling flow reinforces both the heat exchange through the solidification front and the dendrite re-melting or fragmenting, stimulating the formation of an equiaxed crystal at the round bloom center. As the injection mode changes from the five-port nozzle to the six-port nozzle, the superheat degree in the round bloom center at the mold exit decreases by 9.3 K, which is one of the resulting increase in the center equiaxed crystal ratio is about 4.3% and the length of columnar decreases by 20 mm. A weaker impingement of the outlet flow on the shell has been observed as well, which can be expected to eliminate the popular subsurface white band phenomenon with an even shell thickness in the mold region. This suggests that the six-port nozzle can effectively improve the quality of large round bloom casting.