| Recently,the Ni-based superalloy for corrosion resistance is usually manufactured by duplex or triple process,i.e.the raw material are melted and cast into master alloy ingot in a non-vacuum induction furnace,and then the master alloy ingot is remelted and cast into foundry goods.The traditional technology exists some disadvantages like high energy consumption and low yield.The alloy ingots produced usually have defects of coarse grain,severe shrinkage porosity,and serious segregation.Compared with the traditional technology,the continuous casting process consume lower energy and has a higher yield.Therefore,it is meaningful to introduce the continuous casting technology into the production of superalloy.According to the problems existed in master alloy and recent research status at home and abroad,the advantages of the electromagnetic stirring(EMS)and the continuous casting technology are combined in this study,the effects of linear EMS on solidification structure of superalloy Inconel 625 ingot are systematically investigated,and the mechanism of action is analyzed.The research results of characteristics analysis of electromagnetic force distribution in the liquid metal with linear EMS show that,when the structure parameters of linear electromagnetic stirrer keep constant,the electromagnetic force increases as the distance away from the EMS.The electromagnetic force in the melt increases as current intensity increases,and the force first increases then decreases with the increasing of current frequency.In our experiment condition,with a constant current intensity of 150A,the EMS stirring intensity goes highest when the current frequency is 8Hz.The Inconel 625 alloy is melted in a medium-frequency induction furnace,then solidify in a self-designed unidirectional-cooling mold.Different EMS parameters are implemented to the solidifying process,i.e.No EMS;150A,3Hz;150A,5Hz;150A,8Hz;150A,11Hz.The research results of effects of EMS on solidification structure of Inconel 625 master alloy ingot show that,comparing without No EMS,imposing L-EMS to the solidification process of Inconel 625,the equiaxed crystals ratio in ingot is increased the average equiaxed grain size is reduced.When the current frequency is 8Hz,the equiaxed crystals ratio increased from 13%to 84%,and the average equiaxed grain size decreased from 9.2mm to 3.4mm.The temperature changing in the melt is measured and recorded,the temperature data shows that the imposing of EMS can make the inner temperature distribution more uniform,the average temperature gradient decreased from 60K/cm to52K/cm,which is one of the reason why the solidification structure are improved.With EMS,columnar dendrite significantly reduced and growth direction tilted in Inconel 625,besides,the imposing of EMS make the dendrite length shorter and rounder.Optical microscope(OM)and scanning electron microscope(SEM)are applied to analyze the microstructure of Inconel 625 alloy,the main precipitated phases are carbide(MC)and(y+Laves)eutectic structure.The diameter,quantity and area proportion of different kind of phases are counted by IPP software,the result shows that,the quantity and area proportion of(y+Laves)and MC increased form the surface to the center of ingot while the MN keep constant;the imposing of EMS can enlarge the content difference of(y+Laves)between surface and center in ingot.The quantity and area proportion of(y+Laves)and MC is lest when EMS current frequency is 3 Hz,but the MN phase will be lest when current frequency is 5Hz. |
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