The Effect of the Liquid Fe–C Phase on the Kinetics in the Carburization of Iron by CO at 1523 K

Abstract

In order to evaluate the effect of liquid Fe–C alloy produced during the carburization on the kinetics of iron carburization, the rates of carburization of iron by CO–Ar gas mixtures have been measured gravimetrically at 1523 K and the growing rates of the liquid Fe–C layer thickness are also measured. The measurements were made under conditions for which the gas phase mass transfer was negligible. It is found that the weight gains due to the carburization reaction are almost proportional to t 2/3 within experimental scatters. For all runs except that of 1% CO, the liquid phase is observed after the carburization time of 300 s. The liquid phase thickness is found to be almost constant for the first 3.6 ks. After 3.6 ks, the liquid phase thickness starts to increase almost linearly with time. The mechanism to maintain the constant thickness is briefly discussed. The carburization reaction rate is calculated based on the well established decarburization rates and is reasonably agreed with the experimental carburization rate. Compared the experimental results with the calculated liquid phase diffusion rates and the chemical reaction rates, it is confirmed that the ratecontrolling step of the carburization reaction of iron with CO gas at 1523 K is the chemical reaction CO + O_ad→CO₂ at the surface after the liquid Fe–C phase is produced.