Enhanced Carburization of Iron by CH4-containing Gas at 1 573 K

The carburization rate of iron by N-2-11 vol% CH4 gas was investigated at 1 573 K employing an induction furnace in order to minimize the pre-decomposition of methane. Unlike the carburization of iron by CO or CO+H-2 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 H-2 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 (D-C(L)) in liquid iron at 1 573 K to be 3 x 10(-9) m(2)/s. In addition, the moving mechanism of liquid/solid interface was schematically proposed.