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

摘要

To study the substitution of Fe_(3)Si–Si_(3)N_(4) for refractories in the upper RH refiner, this paper simulated the service condition of RH refining and studied the change of the Fe_(3)Si–Si_(3)N_(4) in the simulated condition. A Fe_(3)Si–Si_(3)N_(4) 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 Fe_(3)Si–Si_(3)N_(4) specimen were studied and analyzed thermodynamically and dynamically. The results show that at high temperatures in vacuum, Fe volatilizes from the Fe_(3)Si melt in Fe_(3)Si–Si_(3)N_(4) and reacts with Si_(3)N_(4) on the Si_(3)N_(4) crystal surface, forming new Fe_(x) Si melt there; then Fe continues to volatilize from the new Fe_(x) Si melt, causing Fe_(x) Si alloy particles finer and more uniform in Fe_(3)Si–Si_(3)N_(4); the hexagonal columnar Si_(3)N_(4) crystals begin to decompose partially, and become cylindrical with edges and corners disappearing; during prebaking or operation interval of RH refining, a SiO_(2) film which has better stability than Si_(3)N_(4) is developed on the surface of Si_(3)N_(4) crystals or Fe_(3)Si–Si_(3)N_(4) bricks, preventing the decomposition of Si_(3)N_(4) and improving the application feasibility of Fe_(3)Si–Si_(3)N_(4) in RH refining.