Abstract
The mechanism of nodular oxidation on 13Cr-0.3C stainless steel at the quenching treatment, and the effects of base metal were studied by EPMA and electron diffraction analysis. Nodular oxidation scale was constructed from two layers, outer layer was mainly consisted of Fe-oxide but inner layer included Cr-oxide. Normal and uniform oxidation scale was identified as Cr2O3 film. It was detected that a large quantity of precipitates identified as β-Cr2N or CrN were found on the interfacial surface under the nodular oxidation scale, and that the specimen included larger quantity of N showed higher ratio of nodular oxidation. Nodular oxidation of Fe-Cr alloy did not occur only in case of which the normal scale consisted of Cr2O3 film was cracked to oxidize Fe directly, but in case of inevitable depletion of Cr at the interfacial surface under normal oxidation scale because of preferential oxidation of Cr. From these facts, Cr-nitride was mentioned as one of the factor of nodular oxidation on Fe-Cr alloy. Namely the location where the precipitation of Cr-nitride depleted metallic Cr, that is the effective Cr, under normal oxidation scale growed into the site of nodular oxidation.
