Study On Preparation Technology By Thermodynamics And Performance Of Iron-based Powder Metallurgical Material Containing Nitrogen

Iron nitride has high hardness and good wear resistance,corrosion resistance and magnetic properties.If we replaced iron-base powder metallurgical material with Fe-based powder metallurgy material containing nitrogen,some performance defects of iron-base powder metallurgical material can be improved,so that the lifetime of material shall be extended and the economic benefits shall be improved.The thesis focuses on the preparation technology and performance of Fe-based powder metallurgy material containing nitrogen.The Fe-based powder metallurgy material containing nitrogen was prepared using Fe₃N powder by means of cold isostatic pressing and sintering in a protective atmosphere which was formed by mingling proportional H₂ with N₂.And Fe₃N powder was prepared using nitrified reduced ferric oxide powder but iron powder.The thesis studied on the component,structure,physics and mechanics performance of the Fe-based powder metallurgy material containing nitrogen,and analyzed the process of powder-making and sintering in accordance with diffusion kinetics and thermodynamics.The results show that the Fe-based powder metallurgy material containing nitrogen is composed of Fe and Fe₄N,and the content of Fe₄N is 19%.The material has high density, the electric resistivity is 19μΩ·cm,the saturation magnetization is 86.8emu/g and the coercive forces and remanence are 26Oe and 0.45emu/g respectively.By comparing with the conventional Fe-based powder metallurgy material,the hardness,corrosion-resistance and wearing resistance of the nitride powder metallurgical material are improved by 2～3 times,2～3 times and 1～2 times.The results of thermodynamics show that the nitrified reduced ferric oxide powder is better than iron powder.Fe₄N can also be oxidized under low oxygen partial pressure,so there must be protective atmosphere in the process of sintering.It explains nitrogen potential and the diffusion mechanism of nitrogen atom with sintering kinetics.The sintered materials with plentiful Fe₄N could be prepared by sintering in NH₃-N₂ atmosphere.During the sintering process,NH₃ supplied the nitrogen potential and N₂ reduced the hydrogen partial pressure,so that the nitrogen potential could be controlled.