Precipitation of dendritic M23C6 carbides in alloy 690 during continuous cooling

M23C6 carbides with a distinct dendritic morphology are discovered for the first time in continuously cooled Alloy 690. Branches stretch out from the interfaces of initial carbides, and as much as the fifth order branches come into existence. The dendritic morphology of carbides is mainly resulted from interfacial destabilization, which is closely related to the size of carbides, the relative supersaturation, and constitutional undercooling. In addition, the formation of dendritic morphology is cooling rate sensitive and it cannot appear at a cooling rate lower than 2 °C/min. •M23C6 carbides with distinct dendritic morphology are discovered for the first time of continuously cooled Alloy 690.•The three-dimensional morphology of dendritic carbides is revealed by the method of deep etching.•The formation of dendritic morphology is mainly resulted from the interfacial destabilization of carbides.•The precipitation of dendritic carbides is cooling rate sensitive and it cannot happen at a rate lower than 2 °C/min.