| Abstract: | Carburization of chromium nickel steels in a carbon bed Annealing the samples in carbon powder is a simple method for testing the carburization behaviour of heat resistant CrNiFe steels. It is shown that according to the thermodynamic conditions during this test a very thin layer of Cr2O3 is formed on the surface of the samples in the temperature range 900° to 1050°C. This layer virtually prevents carburization. Above 1050°C. The oxide layer is transformed to a carbide and carburization of the alloy can take place without restraint. However, the influence of temperature on carburization as described may not apply to service conditions, in particular, carburization may also occur if the oxide layer is thermodynamically stable but porous and fissured. Upon carburization carbon is diffusing into the alloy and reacting with chromium and iron under formation of the carbides M7C3 in an outer zone and M23C6 in an inner zone. The penetration of these zones is also determined by the solubility of carbon in the carburized region. By a high nickel content of the alloy the carbon solubility is diminished and therefore the rate of carburization is retarded. This influence of the nickel content also shows under service conditions. |
