Abstract:Nitrogen is one of the undesirable impurity elements of superalloys and it can induce the precipitation of nitrides and the formation of microporosity to worsen the mechanical properties of material. With the increasingly high demands in superalloy component quality, nowadays the nitrogen content in superalloy has been recommended to be no higher than 10×10-6 wt.%. Chromium is an important beneficial alloying element widely employed in superalloys (with an addition up to 20 wt.%) for it can enhance the anti-corrosion performance of alloys at elevated temperature. However, chromium has a high affinity to nitrogen that it could be very hard to achieve a low nitrogen content in high-Cr alloys. Therefore, it is necessary to study the features of the nitrogen-removing process of high-Cr alloys. In this work, the nitrogen-removing process during the vacuum induction melting of a high-Cr nickel based alloy was investigated through thermodynamic calculation and kinetic experiments. Results show that high-Cr nickel based alloy had a high thermodynamic equilibrium solubility of nitrogen, and it was mainly dominated by the vacuum pressure. In order to achieve the goal of [N]≤10 ppm, the melting vacuum pressure should be no higher than 0.1 Pa. To study the kinetic characteristics of nitrogen-removing process, the melted metal was held at 1500, 1550 and 1600 ℃, and sampled at 0, 30, 60, 120, 180 and 240 min at 0.1 Pa after the complete melting of alloy, respectively. Results indicate that nitrogen content dramatically decreased at the beginning of melt holding, but in the medium and later stage it took a much longer period of time to get close to the equilibrium solubility of nitrogen. Kinetic data analysis shows that the nitrogen-removing process of high-Cr nickel based alloy can be classified as the second-order reaction, which reflects that the process was controlled by the chemical reaction on melt surface. The apparent rate constants of nitrogen-removing process at 1500, 1550 and 1600 ℃ were calculated to be 0.0184, 0.0233 and 0.0397 m?s-1 , respectively, and the apparent activation energy was determined to be 211.4 kJ?mol-1.