The effect of the liquid Fe-C phase on the kinetics in the carburization of iron by CO at 1 523 K

In order to evaluate the effect of liquid Fe-C alloy produced during the ca rburization on the kinetics of iron carburization, the rates of carburizati on of iron by GO-Ar gas mixtures have been measured gravimetrically at 1 52 3 K and the growing rates of the liquid Fe-C layer thickness are also measu red. The measurements were made under conditions for which the gas phase ma ss transfer was negligible. It is found that the weight gains due to the ca rburization 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 ma intain the constant thickness is briefly discussed. The carburization react ion 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 rate-controlling step of the carburization reaction of iron with CO gas at 1 523 K is the ch emical reaction CO+O-ad-->CO2 at the surface after the liquid Fe-C phase is produced.