Determination of solid solubility products of [Nb][C] in the case and the core of high-temperature carburizing steel by extraction phase analysis method

In this study, the steels with different carbon content of 0.20 wt% (20C) and 1.0 wt% (100C) were prepared to represent respectively the carburized case and the core, and the solid solubility products of [Nb][C] and NbC precipitates in the steels in the austenitizing temperature range of 1203 similar to 1473 K were analyzed by the extraction phase analysis method. The results showed that the solid solution products of [Nb][C] in the 100C steel were much lower than those calculated from the reported equation, although they were higher than those in the 20C steel. It was also found that the amounts of NbC precipitates in the steels did not decrease evidently when the austenitizing temperature was below 1323 K. The pinning effects of NbC precipitates both in the carburized case and in the core of gear steels after high-temperature carburizing at 1253 K were experimentally proved.