Carburization of Fe-Ni-Cr steels in CH4-H2 mixtures at 850 - 1000°C

Abstract

Three heat resistant FeNiCr steels have been carburized in mixtures of CH 4 + H 2 in the temperature interval 850-1000 °C. The carbon activity in the gas phase was larger than one. Under these conditions, the carburization process involved carbon deposition on the outer surface of the alloy, dissolution and diffusion of carbon into the alloy as well as carbide formation ((Cr, Fe) 7 C 3 + (Cr, Fe) 23 C 6 ). The rate determining step was diffusion of carbon into the alloy. Two models, which both were based on Fick's 2. law, have been applied on the results. Wagner's model for internal oxidation, which give an analytical solution to Fick's 2. law, did not fit the obtained results. With the model based on a finite difference technique, which gives a numerical solution to Fick's 2. law. it was possible to obtain a good fit. However, the kinetical and thermodynamical data used in the calculation deviate from those found in literature.