Study On Gas-Solid Decarburization Dynamics Of Iron Sheet

Research on reaction dynamics of high carbon Fe-C sheet decarburization under ArH₂-H₂O weak oxidizing atmosphere is carried out. The key research content includes the influencing factors on decarburization rate, the distribution of carbon in sheet, the rate controlling step in decarburization reaction.Based on the results, a new method for improving dynamics conditions and decarburization effect is proposed.The factors on decarburization employed are thickness, heating temperature, initial carbon content and holding time, single factor method is used in the study. Initial carbon content of Fe-C sheet is 4.2%,3.2%,the thickness of sheet is 0.6mm,1mm,1.5mm and2 mm respectively,heating temperature is 1293¹413K and heating time is 10⁸0min.The results show that the gas-solid decarburization reaction of Fe-C alloy sheet is a apparent first order reaction. The activation energy of decarburization reaction is144.9KJ/mol, nearly equals to 140KJ/mol, the empirical value of diffusion activation energy of C in austenite phase. The conclusion that the diffusion of carbon in sheet bulk to the reaction interface is the rate controlling step is confirmed by this research. A segmented heating method is created on the basis of research results. By the new method,the carbon content of 2mm Fe-C alloy sheet with initial carbon content 4.15% can decrease to 0.28% after 70 min treating, relative to 0.98% of the constant temperature method.The quantitative relation equations of the rate and factors are derived after the analyse of impacting effect of single factor on reaction rate.The thickness of de-graphite layer has a good linear relationship with 1/2 powers of the time, y=Ct^1/2. Thicker sheet and higher temperature promote the moving speed of degraphite layer. An apparent diffusion coefficient D=3.4³.5×10^-7cm²/s is gained at 1293 K by calculation, agreeing well with empirical diffusion coefficient. This result validated the conclusion of the rate controlling step again.