Carburization of Fe-Ni-Cr steels in CH{sub}4-H{sub}2 mixtures at 850-1000℃

摘要

Three heat resistant FeNiCr steels have been carburized in mixtures of CH{sub}4 + H{sub}2 in thetemperature interval 850- 1000 ℃. The carbon activity in the gas phase was larger than one. Underthese conditions, the carburization process involved carbon deposition on the outer surface of thealloy, dissolution and diffusion of carbon into the alloy as well as carbide formation ((Cr,Fe){sub}7C{sub}3 + (Cr, Fe){sub}23C{sub}6). The rate determining step was diffusion of carboninto 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 theobtained results. With the model based on a finite difference technique, which gives a numericalsolution to Fick's 2. law, it was possible to obtain a good fit. However, the kinetical andthermodynamical data used in the calculation deviate from those found in literature.