2014 Volume 54 Issue 7 Pages 1552-1559
The carburization rate of iron by N2-11 vol% CH4 gas was investigated at 1573 K employing an induction furnace in order to minimize the pre-decomposition of methane. Unlike the carburization of iron by CO or CO+H2 gases, the carburization rate of iron by CH4-containing gas was controlled not by chemical reaction at the surface, but by diffusion of carbon in the liquid phase of Fe–C. The carburization rate by CH4 was about 30 times faster than that by 50 vol% CO. The effects of H2 addition and change in CH4 concentration supported that the chemical reaction do not control the total carburization rate. The formation of graphite rods confirmed that the surface had a very high carbon concentration and the chemical reaction rate is sufficiently fast. Numerical simulation of the carbon diffusion in the spherical iron estimated the diffusivity of carbon () in liquid iron at 1573 K to be 3 × 10–9 m2/s. In addition, the moving mechanism of liquid/solid interface was schematically proposed.