Cooling rate measurements on pure iron rapidly solidified by piston quenching

Abstract

Cooling curves have been monitored during rapid solidification of pure iron, using a rapid response thermocouple embedded in one of the quenching pistons. Cooling rates are found to be typically 106 to 107 K sec−1 in the vicinity of the solidification point at 1500° C, falling to 2 × 104 to 3 × 105 K sec−1 at 500° C. Heat-flow analysis shows that cooling conditions during rapid solidification are clearly non-Newtonian, with heat transfer coefficients of 3 × 105 to 6 × 105Wm−2 K−1 and Nusselt numbers of 0.5 to 1.0. Cooling rates, heat transfer coefficients and Nusselt numbers are higher for piston quenching than for other rapid solidification processes such as melt spinning. Piston-quenched iron microstructures can be ferritic or martensitic depending on the cooling rate during rapid solidification.