Concomitant Precipitation of Intermetallic -NiAl and Carbides in a Precipitation Hardened Steel

The investigated steel is hardened by precipitation of both intermetallic beta-NiAl particles and carbides. Around peak hardness, here reached after aging at 520 degrees C for 6 h, the number density of beta-NiAl particles is 2.4 x 1024 and 4.4 x 1023 for carbides, respectively. The carbides and beta-NiAl often form co-precipitates with presumably the carbides nucleating on the beta-NiAl precipitates. The secondary carbides are mainly of the Cr-rich M23C6 type in the investigated states. The steel has a good resistance against over-aging, whereby the beta-NiAl coarsen considerably slower than the carbides.