Thermodynamics and Kinetics of Deoxidation and Denitrification in Vacuum Induction Melting of C-HRA-3 Nickel-based Heat Resisting Alloy

Author of the article:LI Longfei, LIN Tengchang, LIANG Qiang, HE Xikou, CHEN Zhengzong, CHEN Kun

Author's Workplace：Central Iron and Steel Research Institute, Beijing 100081, China

Key Words：C-HRA-3 heat resistant alloy; deoxidation; denitrification; thermodynamics and kinetics; vacuum induction melting

Abstract：In order to explore the thermodynamic law of the deoxidation and denitrification of C-HRA-3 nickel-base heat-resistant alloy by vacuum induction melting, high purity alloy raw materials were melted by VIM-50 vacuum induction furnace. The smelting conditions were strictly controlled. Samples were taken for monitoring and analysis. The results show that with the increase of refining temperature, the equilibrium carbon and oxygen product in C-HRA-3 alloy solution increases, while the nitrogen equilibrium solubility decreases. The vacuum degree is increased while the equilibrium solubility of oxygen and nitrogen is reduced. Under the experimental smelting condition (1 582 ℃, 2.7 Pa), the equilibrium [O] and [N] contents are 3.73×10-4% and 23.66×10-4%, respectively. With the prolongation of refining period, [O] and [N] contents gradually decreased, and the content of [O] increased twice due to the influence of MgO crucible decomposition in later refining period. The limiting links of vacuum carbon deoxidation and denitrification of C-HRA-3 alloy are the diffusion of [O] in the liquid boundary layer and the chemical reaction of [N] atoms at the interface, respectively. The calculated average mass transfer coefficient k[O] in the liquid boundary layer is 2.68×10-3 cm/s. The denitrification reaction is a second-order reaction with an apparent rate constant of 0.733 cm/s.