Investigation On Denitrogenation Technology And Mechanism During VIM Refining Ni-base Superalloy

Ni-base superalloy is a key material to make turbine engine, not only in aeroturbine and the kind of high temperature part of astronautical rocket engine, but also in power, metallurgy and chemical industry and so on.The chemical composition is the core problem in superalloy research, and the trace element is the hot topic in chemical composition research, too. The nitrogen is one of main impurity elements, it has the disadvantageous influence to the performance of superalloy. So reducing the content of nitrogen in superalloy is very important for developing the career of superalloy in our country.The denitrogenation behavior during vacuum induction melting of Ni-base superalloy using CaO crucible has been studied and the influence on denitrogenation through changing the vacuum degree and the melting time has been analyzed too. The optimal melting technology and the shapes of nitrogen have been confirmed. During the melting process the change of the content of oxygen and sulfur has been analyzed. Through the value of nitrogen after joining the aluminum and the titanium, the influence of the elements of aluminum and titanium on denitrogenation has been confirmed (e_N^Ti≈-0.38) and the interaction coefficient of titanium to nitrogen and the equilibrium constant of reaction have been calculated, too, (K₁= （0.064 ¹.67）×10^-4 m/s, K₂= （3～98）×10^-2 m/s·%). Whereas the results of the experiment, the denitrogenation mechanism is proved as the value of nitrogen content is less than 5×10^-4 （mass fraction, %）. It is a mixed process that can provide the theory of further reduces the value of nitrogen in the Ni-base superalloy and the process of movement of nitrogen in liquid is the main controlling factor.