Investigation into deoxidation during vacuum induction melting refining of nickel base superalloy using CaO crucible

摘要

The influence of carbon and aluminium on deoxidation during vacuum induction melting (VIM) of a Ni - 6Cr-2Mo - 6W - 5Co alloy using a CaO crucible has been studied. It has been found that carbon plays a dominant role in deoxidation during the melting stage, and about 50 - 70 percent of the initial oxygen can be removed. Thermodynamics calculations show that the C -O reaction is far from the equilibrium state, and experimental results for carbon and oxygen contents in the liquid alloy correspond with those when the CO partial pressure p_(Co) is 10~3 -10~2 Pa. Aluminium addition can further reduce the oxygen content to below 6 ppm. Thermodynamics calculations for the C - Al, Al - CaO and C - Al_2O_3 reactions demonstrate that they can all take place during the melting process. These reactions bring about reductions in the amounts of carbon and aluminium, respectively, of about 1.3 - 3.5 times and 20 - 50 times those required for deoxidation only.