| Recently, the Ni-based superalloy for corrosion resistance is usually manufactured by two or three kinds of technology, i.e. the raw materials are melted and casting into a master alloy ingot in a non-vacuum induction furnace, and then the master alloy ingot is re-melted and casting into foundry goods? There exist some disadvances of high energy comsuption and low yield in the traditional technology. The alloy ingots produced usually have defects of coarse grain, more shrinkage porosity, and more serious segregation. Comparing with the traditional technology, there exist some advances of low energy comsuption and high yield in continuous casting. Therefore, it is meaningful to introduce the continuous casting technology into the production of superalloy. This paper is financially supported by National Natural Science Foundation of China (No.50834009) and the Foundamental Research Funds for the Central Universities (No. N090609001). According to the problems existed in master alloy and recent reaearch status at home and abroad, combining the advantages of the electromagnetic stirring(EMS) and the continuous casting, the effects of EMS on quality of superalloy Incoloy 800 ingot are systematacially investigated, and the mechanism of action is analysed. And then, Incoloy 800 rectangular billets with no defects are produced by vertical continuous caster in laboratory. This is the first time to achieve continuous casting of superalloy at home.The research results of characteristics analysis of electromagnetic force in the liquid metal with EMS show that, when the structure parameters of linear electromagnetic stirrer keep constant, the electromagnetic force increases as the distance away from the EMS decreases. The electromagnetic force at some point in the melt increases as current intensity increases.And the forece first increases, and then decreases with increasing current frequency. The melt is affected by the electromagnetic force along the circumferential direction and the force along the radial direction, but the rotational flow in the melt is mainly affected by the force along the circuferential direction with rotaring electromagnetic stirring(R-EMS). With the same structure parameters of electromagnetic stirrer, magnetic field intensity decays rapidly as depth in the melt increases, and its decay is measured by the penetration depth. The penetration depth is deeper, it means that magnetic field intensity dacay slowly and the area affected by magnetic field is larger. The penetration depth is related to the frequency and polar pitch of the stirrer.The reaseach results of effects of on EMS on quality of Incoloy 800 master alloy ingot show that, comparing without EMS, imposing L-EMS to the solidification process of Incoloy 800, the equiaxed grain average size in ingots is reduced from 3.5mm to 2.3mm, the equiaxed crystals ratio is increased from 5% to 43%. And imposing R-EMS to the solidification process of Incoloy 800, the equiaxed grain average size in ingots is reduced from 3.5mm to 1.9mm, the equiaxed crystals ratio is increased from 5% to 48%. The length of central shrinkage porosity is reduced from 70mm to 48mm, and the shrinkage pososity ratio is decreased from 37% to 25% with L-EMS. The length of central shrinkage porosity is reduced from 70mm to 43mm, and the shrinkage pososity ratio is decreased from 37% to 23% with R-EMS.The solute element microsegregation and macrosegregation in ingots are effectively improved and the element distribution is more uniform with EMS. The L-EMS causes that column grains happen to incline in the longitudinal plane, the R-EMS causes that column grains happen to incline in the horizontal plane. The micro structure without EMS consists of the equiaxed dendrites in chilled layer, the unidirectional dendrites in inner surface, the unidirectional dendrites near center and the cross dendrites in the center. The microstructure with EMS consists of the equiaxed dendrites in chilled layer, the unidirectional dendrites in inner surface, the cross dendrites in the center, the fine equiaxed dendrites in the center and the dendrites with arms in the center. The fragmentation and drift process of dendrites are both caused by the fusing theory and break theory in our research, and the process is proved according to the dendrite morphology and main element composition in dendrites trunk. The fragmentation and drift process and constitutional supercooling cause the grains refined.The research results of effects of on EMS parameters on quality of Incoloy 800 ingots show that, the equiaxed grain average size in ingots first increases, and then decreases as magnetic field increases. And the equiaxed crystals ratio first decreases, and then increases as magnetic field increases. When the magnetic field is 1.73kQ the quality of ingot is best. The quantity of Ti(CN) in ingot is decreased as magnetic field increases, it means EMS is good to remove the Ti(CN). Based on the vertical continuous caster with EMS, Incoloy 800 rectangular billet without slip angle depression and the longitudinal cracks can be produced. The duration of melt affected by L-EMS is more advanced as withdrawal speed increases. The equiaxed crystals ratio in rectangular billet is increased, and the equiaxed grain average size in rectangular billet is reduced. It means that the technology of EMS can increase the equiaxed crystals ratio in rectangular billet produced in continuous casting. Furthermore, the inner quality of slab can be improved. |
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