Solidification modes and microstructure of Fe–Cr alloys solidified at different undercoolings

The solidification mode and the solidified microstructure of Fe–Cr alloys at various undercoolings have been studied with the electromagnetic levitation method. Different solidification modes have been observed. The undercooling ranges for the different solidification modes have been identified. For undercoolings smaller than about 180–200 K, a dendritic solidification mode was observed, for undercoolings between 200–220 K and 250–270 K, a cellular solidification mode was detected, while for undercoolings larger than about 260–280 K, a planar front solidification mode produces microsegregation-free microstructure. The preference for the formation of the equilibrium BCC phase rather than the metastable FCC phase in solidification at large undercoolings is discussed on the basis of nucleation temperature and dendrite growth velocity calculations.