In present paper, a ladle–tundish–mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring(MP) process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring(SP) and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.
A ladle-tundish-mould transportation model considering the entire multiple pouring(MP) process is proposed. Numerical simulation is carried out to study the carbon distribution and variation in both the tundish and the mould for making a 292 t steel ingot. Firstly, the fluid flow as well as the heat and mass transfer of the molten steel in the tundish is simulated based on the multiphase transient turbulence model. Then, the carbon mixing in the mould is calculated by using the species concentration at the tundish outlet as the inlet condition during the teeming process. The results show a high concentration of carbon at the bottom and a low concentration of carbon at the top of the mould after a MP process with carbon content high in the first ladle and low in the last ladle. Such carbon concentration distribution would help reduce the negative segregation at the bottom and the positive segregation at the top of the solidified ingot.
The structures in vacuum-assist high-pressure die casting(HPDC) AM60 B alloy were studied by using an optical microscope and a scanning electron microscope with an energy dispersive spectrometer.It was found that the HPDC under the vacuum could significantly change the morphology and distribution of the microstructure.For both conventional and vacuum-assist HPDC processes,the externally solidified crystals(ESCs) tended to aggregate in the center along the thickness direction of the castings.Besides,the aggregation was more pronounced,and the number of ESCs decreased,and the ESCs tended to become smaller and more globular,as the distance between the specimen location and runner increased.Compared with the conventional castings,the vacuum-assist HPDC can significantly reduce the size and amount of ESCs,and the ESCs tended to be more globular.For the distribution of ESCs along the thickness of the specimens,the aggregation tendency was more pronounced in vacuum-assist die castings than that in conventional castings.Besides,the distribution of ESCs at different locations was more converged in the vacuum-assist HPDC than that in the conventional HPDC.
