Quantitative analysis of carbon content in cementite in steel by atom probe tomography

Atom probe performance in the quantitative analysis of carbon atoms in steel was investigated through analysis of stoichiometric spherical cementite (Fe3C) in steel. The carbon concentration was estimated by determining the mean carbon number of molecular ions having a mass-to-charge ratio of 24. The apparent carbon concentration of cementite increased as the specimen temperature decreased, and it was several at% higher than the stoichiometric value (25 at%) under the preferable condition of low specimen temperature. On the other hand, the apparent carbon concentration was not changed by pulse fraction. These results indicate that the large deviation from the stoichiometric value did not arise from the preferential retention and evaporation between carbon and iron. The other mechanisms explaining the phenomenon have been discussed.