Investigation On Nitridation Mechanism Of Ferrosilicon And Its Influencing Factors

Ferrosilicon nitride is a kind of alloy that can provide cheap nitrogen source.In recent years,the rapid development of microalloy steel and alloy steel makes it a promising application.At present,a domestic alloy production enterprise uses the direct nitriding method to produce ferrosilicon.In the process of production,the nitrogen increase is volatile.The nitrogen content is sometimes difficult to meet the requirements of the national standard.It is imminent to make clear the mechanism of direct nitriding of ferrosilicon and optimize the process parameters.In this paper,the thermodynamics,kinetics and phase evolution of FeSi75 nitriding process were studied systematically.The effect of additives on the nitrogen increase was also investigated.The results can provide theoretical support for the improvement of the production process of ferrosilicon nitride.The phase equilibrium diagram of the ternary Si-O-N system and the quaternary Si-O-N-Fe system at different temperatures was plotted by FactSage software.It was found that the higher the reaction temperature is,the higher the initial nitrogen partial pressure of Si₃N₄ generating is,and the lower the oxygen partial pressure is.When the oxygen partial pressure is relatively large,there is Si₂N₂O in the products.The effects of reaction temperature,holding time and additives on the nitriding of ferrosilicon were studied experimentally.The results show that the nitrogen content of ferrosilicon nitride increases with increasing reaction temperature and prolonging holding time,but the increasing trend is getting less and more obvious.The nitrogen increase,the average pore size of the spherical ferrosilicon nitride increase with increasing the proportion of hydrogen carbonate in the additive.The yellow dextrin in additive has no obvious effect on the above indexes,however,the compressive strength of the spherical ferrosilicon increases with increasing the proportion of yellow dextrin.The results of the XRD analysis show that the Si element in FeSi75 was transformed from Si→α-Si₃N₄→β-S_i3N₄.Fe was transformed from FeSi₂→FeSi→Fe₂Si→Fe₃Si in the process of nitriding.The kinetics of the nitriding process was analyzed by using the"Corpuscular model".The restrictive step of the direct nitriding process is the porous diffusion.