Abstract
A three-dimensional numerical model combining electromagnetic field, fluid flow, heat transfer, and solidification has been established to study the effect of nozzle injection mode and mold electromagnetic stirring (M-EMS) on the internal quality of a continuously cast bloom. The model is validated by measured data of the magnetic flux density along the stirrer center line. According to the simulation and experimental results, M-EMS can introduce a horizontal swirling flow ahead of the solidification front, promoting the superheat dissipation of molten steel and columnar to equiaxed transition (CET). As the stirring current increases from 0 to 800 A, the superheat at the mold exit in the bloom center decreases by 1.9 K for the single-port nozzle case and 3.8 K for the five-port nozzle case. The resulting increase in the equiaxed crystal ratio is about 5.65% and 4.06%, respectively. In comparison, the injection mode shows a more significant influence on the heat transfer and solidification structure in the bloom under the present casting conditions. The superheat at the mold exit in the bloom center decreases by 5.1‒7.7 K as the injection mode changes from a single-port nozzle to a five-port nozzle, and the increase in the equiaxed crystal ratio ranges between 14.8% and 17%. It is found that the flow velocity of the molten steel in front of the solidification interface for the five-port nozzle is higher than that for the single-port nozzle regardless of the M-EMS power. The washing effect here reinforces both the heat exchange through the solidification interface and the dendrite re-melting or fragmenting, stimulating the formation of an equiaxed crystal at the bloom center. In addition, it is observed that both the central shrinkage and carbon segregation have decreased with the five-port nozzle plus M-EMS. This suggests that the combined application of a five-port nozzle and M-EMS can effectively improve the internal quality of large bloom castings.
Highlights
The quality of special rolled steel products is closely related to the control effect of the as-cast macrostructure and composition uniformity
mold electromagnetic stirring (M-EMS) is a widely accepted technique used to optimize molten steel flow in bloom casting; the swirling flow driven by the rotating electromagnetic force improves the heat transfer at the solidification front, which has been proven to enhance the columnar to equiaxed transition (CET) during solidification
It is evident that the model calculation results are in good agreement with the measured values when the temperature of copper tube is 298 K, which proves that the model is accurate and reliable
Summary
The quality of special rolled steel products is closely related to the control effect of the as-cast macrostructure and composition uniformity. Applied a 3D numerical model to analyze the molten steel flow with M-EMS for a round strand, in which the operational parameters for the current, frequency, and nozzle submerged depth were determined for an improved round strand quality. A 3D coupling numerical model of electromagnetic, flow, heat transfer, and solidification in the mold region is established by taking the example of a 410 mm × 530 mm bloom casting for carbon 45 steel bar production. The 3D coupling analysis has been carried out together with industrial casting experiments, which is expected to reveal the influence of the stirring current intensity in the conventional single-port nozzle and a newly designed five-port nozzle injection modes on the macro-solidification structure of large bloom castings
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