Crystallographic relationships between δ-ferrite and γ-austenite during unidirectional solidification of Fe-Cr-Ni alloys

Abstract

The crystallographic orientation relationships between δ-ferrite and γ-austenite during unidirectional solidification of Fe-Cr-Ni alloys have been evaluated with EBSPs (Electron Back Scattering Patterns). The preferred orientation relationship between δ and γ agrees with the Kurdjumov-Sachs (K-S) relationship in both rod and lamellar eutectic structures obtained by Bridgman experiments. It is thought that the preferred relationship is developed by nucleation of secondary phase. The orientation relationship between primary γ-dendrites and primary δ-dendrites during dissimilar alloy welding (primary γ to δ-dendrites) by a laser experiment also agrees with the K-S relationship. The transition from primary γ to δ-dendrites is thought to be controlled by heterogeneous nucleation of ferrite at the growing γ-dendrite front. It is suggested that the nucleation also plays an important role in the microstructure formation.