Kinetics study of nitrogen removal from liquid IN718 alloy during vacuum induction melting

The kinetics of nitrogen removal from the molten IN718 alloy has been investigated by the sampling method under reduced pressure. The effects of initial nitrogen concentrations, alloying elements (carbon, titanium, and aluminum), and the intensity of inductive stirring on the nitrogen removal are discussed in the temperature range from 1773 to 1923 K. Experimental results indicate that the nitrogen removal is a 1.5th-order reaction at different initial nitrogen concentrations and temperatures, and the nitrogen removal reaction is controlled by a mixed interfacial and diffusion process. Moreover, the nitrogen removal reaction can be accelerated when the [C]+[O] = CO(g) reaction exists in the melt, and the kinetics changes gradually from a 1.5th-order reaction to a second-order reaction with increasing temperature from 1773 to 1873 K. The nitrogen removal is a second-order reaction in low-speed stirring. Meanwhile, the rate constant of nitrogen removal under the condition of where the mass transfer resistance in the gas phase is negligible, is evaluated. The rate constant of the nitrogen removal increases with increasing temperature. It is also found that titanium decreases the rate constant of nitrogen removal, and aluminum and carbon significantly increase the rate constant of nitrogen removal.