Study On The Preparation And Application Of New Type Corundum Crucible For Smelting Superalloy

In order to improve the purity of superalloys,a new type of corundum crucible for smelting superalloys was prepared and used to carry out the purification smelting test of K417 G recycled ingot.This new type corundum crucible was prepared by gelcasting process using the tabular alumina as raw materials.The effects of the gelcasting process on the microstructure and properties of the corundum crucible were studied systematically using scanning electron microscopy,X-ray diffraction,oxygen-nitrogen analyzer and other test methods.In addition,the existing form of N element in the K417 G recycled ingot and the deoxidation and denitrification mechanism during smelting superalloys in the corundum crucible were studied.Moreover,the physical and chemical interaction of the interface between the crucible and the melt was studied.The conclusions are as follows:The optimized gelcasting process of the corundum crucible is as follows: the grain size distribution of the tabular alumina with size of 1~3mm,0.045~1mm and below0.045 mm is 33:45:22(wt.%).The amount of dispersant is 0.6wt.% of the tabular alumina with size of below 0.045 mm.The solid content of the mixed slurry is 80 vol.% and the amount of monomer and cross-linker is 2wt.% and 0.1wt.% of the total tabular alumina,respectively.The amount of initiator and catalyst is 4.6wt.% and 5.4wt.% of the monomer,respectively,and the gel curing conditions is in 50℃ water bath.The performance test results of the corundum crucible show that its bending strength is 30.5MPa and the thermal shock stability is more than 50 times.The microstructure analysis results show that no reunited particles,obvious cracks,larger size pores and other defects appear in the corundum crucible.The phase analysis results prove that the various additives such as dispersant,monomer and cross-linker,initiator and catalyst added to the crucible during the molding process have been excluded completely.The results of microstructure analysis prove that the N element is present predominantly in the form of nitrides or carbonitrides at the cores of the MC-type carbides in the K417 G recycled ingot.The purification smelting test of K417 G recycled ingot with corundum crucible shows the O and N contents in the ingot can be reduced from0.0017 wt.% and 0.0018 wt.% to 0.0006 wt.% and 0.0008 wt.%,respectively,by melt treatment at high temperature more than 1700℃ for 5min holding time dissolving the nitrides or carbonitrides first and then at 1550℃ low temperature for 20 min holding time removing the oxygen and nitrogen in the 10 Pa vacuum environment.The thermodynamics analysis prove that the content of O and N can be reduced to 1.40×10-4wt.% and4.46×10-4wt.% using corundum crucible to smelt the K417 G recycled ingot by the purification smelting process mentioned above.The analysis results of the interface between the crucible and the melt prove that the corundum crucible has high density and good chemical stability.