Pre-oxidation treatment to increase the service life of heat treatment furnace conveyor belts made of AISI 330Cb Industrial application
The conveyor belts used in the heat treatment furnaces in 330Cb steel have a limited lifetime.
The alloy 330Cb (Fe-34Ni-23Cr-1Nb-1.55Si) is generally used in high temperature carburizing and carbonitriding conditions. These environments induce severe conveyor units degradation due to a quick alloy weakening.
To improve the alloy carburization resistance it is assumed that the presence of an adherent oxide scale acts as a carbon and nitrogen diffusion barrier. The 330Cb oxidation leads to a chromium oxide which is a good diffusion barrier under isothermal conditions. The external manganese chromite can limit the chromium oxide evaporation at temperatures higher than 1000 °C. Important oxide layer degradation occurred after cooling to room temperature.
Recent search has shown that silica acts like a protective/adherent oxide and improves the carburizing resistance.
Formation of the protective silica layer (amorphous or crystallized) is promoted by:
-alloys with silicon content (1.00-2.00%),
-alcaline conditions (a low NaOH concentration)
-and low oxygen containing gaseous environments.
This paper concerns the application of the pre oxidation treatment on an industrial conveyor belt.