The carburizing behaviors and mechanisms for Cr35Ni45Nb alloy subjected to different service conditions were studied in a high-temperature vacuum environment. Generally, the carburizing process of an alloy is always accompanied by diffusional heterogeneous reactions regardless of the service condition of the alloy. For a carburized original tube, there is a layered structure at the inner wall of the tube, which is comprised of a M7C3 zone, a M7C3–M23C6 mixed zone, and a M23C6 zone with different morphologies. However, for a 6-year tube (short for a tube serviced for 6 years), the composite oxide layers formed previously act as effective barriers to carbon infiltration. Moreover, the Cr2O3 scale tended to be carbonized to form carbide scale to spall from the surface in a reducing environment, while the SiO2 kept stable all along. Once the oxide layers were removed or carbonized enough, inconceivable internal carburization occurred widely.
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The authors are grateful for the financial support and facilities provided by China Special Equipment Inspection and Research Institute and Beijing Institute of Aeronautical Materials, respectively.
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Peng, Y., Zhang, M., Xiao, J. et al. Investigations on carburizing mechanisms of Cr35Ni45Nb subjected to different service conditions in a high-temperature vacuum environment. Journal of Materials Research 30, 841–851 (2015). https://doi.org/10.1557/jmr.2015.46