Effect Of Oxide Additives On Iron Carbide Preparation By Two-step Method

With short flow route process steelmaking swiftly arising and shortage of high quality scraps, iron carbide has been concerned widely as its unique phisics and chemistry feature as well as production conditions, and as an excellent replacement of scrap. In this paper, the recent research status on preparing iron carbide and the effects on formation of iron carbide are summarized elaborately, such as reacting temperature, reduction atmosphere, microstructure of raw material, gangue component, deposition of carbon, sulfur-contained gas, etc. In order to settle the problem of low reaction rate, low production efficiency and a mass of dissociative carbon in final reaction time which is harmful for the formation and stability of iron carbide, study of influence of oxidation addition, reacting temperature and carburization atmosphere on iron carbide formation using two-step method is carried out. The main conclusions are as follows:1. The effect of the oxide additive with mass percent be 1% on formation of iron carbideFixing the content of oxide additive be 1 percent, the reduction and carburization experiment was carried out in which iron ore ball with different oxide additives (such as V₂O₃, Al₂O₃, TiO₂, Cr₂O₃, MnO, SiO₂) reacted with H₂-CH₄ or H₂-(CH₄, N₂) in the temperature range from 873 K to 1073 K. After the samples were analyzed by TG, some conclusions could be summarized as follows:(1) V₂O₃ has a well promoting effect on both reduction of iron ore and carburization of reducing iron., but TiO₂ has a retarding effect on them, and SiO₂, Cr₂O₃, MnO nearly have no effect on them. The two reactions can be promoted by Al₂O₃ to some extent, but the effect is not stronger than that of V₂O₃.(2) In the temperature range from 923 K to 1023 K, with temperature increasing, the reduction rate of Australian ore increases obviously. Farthermore, with temperature increasing to 1073 K, the reduction rate increases only a little.(3) Increasing temperature makes against carburization reaction, and carburization reaction has the lowest temperature need. When temperature is lower than 873 K, carburization reaction will not happen.(4) In carburization step, the appropriate contents of N₂ with different additives are as follows: to specimens without additive or with 1 percent of Cr₂O₃, it shouldn't fill the carburization gas with N₂, or the content of it should be within 20 percent; to ones with 1 percent of TiO₂, SiO₂, MnO or Al₂O₃, appropriate content of N₂ is 40 percent; and to specimens with 1 percent of V₂O₃, 60% is the right content.2. The effect of V₂O₃ and Al₂O₃ additives with different contents on formation of iron carbideBrazilian ore was selected as raw ore. The experiment of reduction and carburization was carried out using pellets with 0.25, 0.5, 0.75, 1, 2, 3 mass percent of V₂O₃ and Al₂O₃ respectively. After the samples were analyzed by TG and XRD, some conclusions could be gotten as follows:(1) When the content of V₂O₃ is within 1 percent, with its content increasing, the rates of reduction and carburization increase; When the content of V₂O₃ is 2 or 3 percent, the reduction rate is a little smaller than that of 1 percent, and the increasing trend of carburization rate is also weaker than that within 1 percent.(2) When the content is in the range from 0.5% to 3%, Al₂O₃ has a promoting effect on both reduction and carburization. Especially, there is a well promoting effect when the content is above 1%. Compared with the pellet with V₂O₃, there is no obvious carbon deposition using pellet with 3 percent of Al₂O₃.(3) XRD analysis indicates that metal iron decomposed by iron carbide was found in specimen with 0.5 percent of V₂O₃, however, there was metal iron existing in the specimens with 0.5 or 3 percent of Al₂O₃.3. Study on the reaction kinetics of promoting iron carbide formation by V₂O₃ additiveAustralian ore was selected as raw ore. The kinetics experiment of reduction and carburization was carried out using pellets with 1 mass percent of V₂O₃ in the temperature range from 873 K to 1073 K. It is found that the shrinking-core mode can be utilized for present experiment condition, and the function between reacting time and the rate of progress can be calculated as 1 - (1 - x )^1/3= Kt by the model. From activation energy counted out from the experiment, the following conclusions can be gotten: V₂O₃ has a weakly promoting effect on reduction of iron ore but a strongly promoting effect on carburization of reducing iron. The reaction activation energy decreased from 38.9 kJ/mol to 26.9 kJ/mol after the addition of V₂O₃ with the minishing extent was 31%.