Precipitate behavior in Fe-20Cr-30Ni-2Nb austenitic heat-resistant steel

Abstract

In this study, the precipitation behavior of a new austenitic heat-resistant steel (Fe-20Cr-30Ni-2Nb, in at%) was investigated. The effects of alloying addition of boron (B) and lanthanum (La) on the microstructure of the austenitic steel were scrutinized using SEM, EPMA, TEM, and XRD. The results showed that the addition of B enhanced the precipitation of bar-type Laves phase. A small precipitate with high La concentration was observed at the grain boundary in the alloy without aging; similar precipitates without La also presented in region adjacent to the La single phase. This result indicates that La can exist independently and does not contribute to the formation of new compounds. However, in both Band La-modified alloy, B appeared in the precipitate free zone. In the alloy containing both B and La, only Fe2Nb Lavesphase precipitates, as indicated by the XRD result.