Abstract
Microstructures of steels during unidirectional solidification in zone melting have been investigated by mainly observation of solid/liquid interface.
The solidification rate was in the range of 3-60×10-4cm/sec. Fe-C and Fe-S systems were mainly investigated, and the specimen dimension was 35mm in diameter and 600 mm in length.
After observations of solidification structures, the formation and stability of solid/liquid interface were discussed theoreticaly under the consideration of solute redistribution and thermal flow.
With increase of the supercoal in liquid iron near the interface, solidification front changes from planar to cellular, and finally to dendritic form. Critical conditions for this interface transitions were determined by solute concentration, solidification rate, and temperature gradient. Especially the interfacial tension between solid/liquid iron was intended as a primary foctor for cellular-dendritic transition.
The interfacial tension of iron containing carbon was estimated around 200-600 erg/cm2 with measurement of interfacial curvatures.
There was a good agreement between experimental observations and theoretical estimations for critical conditions of interface transitions.
