Investigation on Morphology Evolution and Phase Interactions of Fe-containing Si₃N₄ in Vacuum High-temperature Environment

Abstract

To study the substitution of Fe₃Si–Si₃N₄ for refractories in the upper RH refiner, this paper simulated the service condition of RH refining and studied the change of the Fe₃Si–Si₃N₄ in the simulated condition. A Fe₃Si–Si₃N₄ specimen prepared by flash combustion was put in a vacuum sintering furnace with carbon lining, fired at 1450°C under 80 Pa of vacuum degree for 2 h, and then cooled. The morphological evolution before and after being treated and phase interactions of the Fe₃Si–Si₃N₄ specimen were studied and analyzed thermodynamically and dynamically. The results show that at high temperatures in vacuum, Fe volatilizes from the Fe₃Si melt in Fe₃Si–Si₃N₄ and reacts with Si₃N₄ on the Si₃N₄ crystal surface, forming new Fe_xSi melt there; then Fe continues to volatilize from the new Fe_xSi melt, causing Fe_xSi alloy particles finer and more uniform in Fe₃Si–Si₃N₄; the hexagonal columnar Si₃N₄ crystals begin to decompose partially, and become cylindrical with edges and corners disappearing; during prebaking or operation interval of RH refining, a SiO₂ film which has better stability than Si₃N₄ is developed on the surface of Si₃N₄ crystals or Fe₃Si–Si₃N₄ bricks, preventing the decomposition of Si₃N₄ and improving the application feasibility of Fe₃Si–Si₃N₄ in RH refining.