Cyclic Oxidation Plus Carburization of Heat-Resistant Alloys Available to Purchase

Nine heat-resistant alloys were exposed to cycles of oxidation plus carburization. Each cycle consisted of 4 h of oxidation in air at 700°C followed by 16 h of carburization in hydrogen gas (H₂) + propylene (C₃H₆) at 950°C. The alloys were tested for 1, 3, and 5 cycles, and invariably were found to have undergone internal carburization. The rate of this process was measured with respect to cumulative carburization time, and the kinetics were found to be parabolic. Data from isothermal carburization of the same alloys were compared with rates found in the cyclic process. In general, the internal carburization produced by the 3- and 5-cycle runs was greater than that resulting from isothermal carburization. This was a result of a “metal dusting” attack of the alloys and increased carbon activities in their surface regions.