| Based on rich manganese resource, Zunyi Ferroalloy Company Limited in Guizhou is the most enormous manganese ferroalloy base in our country, and also one of the key ferroalloy corporations in metallurgy industry of China. It is the only one that has been made mining, dressing, sintering, smelting and refining a coordinated process by 50 years building. The equipment capacity of Zunyi Ferroalloy Company Limited is about 220 kilo-ton yearly, and the main products produced by that are manganese-silicon ferroalloy, silicon ferroalloy, chromium ferroalloy, high, medium and low carbon manganese ferroalloys (about 24~25 kilo-ton yearly), metal manganese (about 4.5~5.0 kilo-ton yearly), and so on. There is a considerable amount of powder (less than 10 mm) as a result of manganese ferroalloy breaking to be exploited. Nitriding the powder may be the best one of multipurpose utilization for both meeting the requirements of steelmaking for the nitrided manganese ferroalloy and making the local rich resource into economy prosperity. Meanwhile, it is important to kwon the interaction between nitrogen and manganese, the nitrogen diffusion in solid manganese, and other effect factors by the experimental study of the metal manganese and low and medium carbon manganese ferroalloy nitrided at various conditions. Based on the researches in domestic and aboard on both the manganese ferroalloy nitriding and manganese- nitrogen system, the influence of time, temperature, and grain size on the solid metal manganese nitriding was studied by means of vacuum resistance furnace, X ray diffraction technique and LECO TC-436 Oxygen/Nitrogen Determinator. Several relationships on nitriding have been discussed by means of thermodynamics computation. Based on reasonable assumption, a mathematic model was set up for metal manganese nitriding. The conclusions are shown as follows:(1) Metal manganese and low and medium carbon manganese ferroalloy can be both nitrided and oxidized in industrial scale nitrogen atmosphere at 1 123~1 223 K for 72 hrs with the product Mn4N and MnO respectively. The finer the powder size is, the more amount nitrogen pick-ups. Moreover, with the nitriding temperature rising, the sample pick-ups increases correspondingly, and so the oxygen content.(2) It is unavoidable that manganese will be oxidized in the nitriding atmosphere because there is considerable oxygen content in the industrial scale nitrogen. Even added as much as 20% ammonia in the nitrogen, the manganese can't be prevented from oxidized effectively. Therefore, it is necessary that the nitrogen as nitriding atmosphere be deoxidized before entering the vacuum resistance furnace by a suitable processing.(3) Based on the thermodynamic computation for the chemical reactions during manganese ferroalloy nitrided, it is shown that the oxygen pressure needed for manganese oxidized is especially minute, therefore, it is unavoidable that manganese will be oxidized in the nitriding atmosphere furnished even by ultrahigh purified nitrogen. Moreover, the low valence manganese oxide can be further turn into high valence oxide, if the remaining oxygen in the nitriding system is enough much. (4) Besides the temperature elevating below 845 K for Mn and lowering from 729 K for Mn4N, it is known that the hydrogen added into nitriding atmosphere can effectively inhibit the manganese, iron, and the nitrides oxidized by thermodynamics analysis. (5) The standard Gibbs energy expressions of formation for both ???-Mn4N and ??-Mn4N are deduced respectively based on the relative thermodynamic data and the regular solution model. Moreover, a precise discuss has made on the equations for reliability and reasonability. (6) The both JMn97 and DJMn-A metal manganese samples with different grain size are nitrided in ultrahigh purified nitrogen at various temperature and time in which a small amount ultrahigh purified hydrogen is added. The conclusions are shown as follows:The finer the powder size is, the faster the nitriding speed, the more amount nitrogen pick-ups. More...
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