Abstract
Unidirectional solidification of iron-cementite ally (Fe-4.28%C-3.86%Cr) was experimented under the following controlled conditions : the temperature gradient in the liquid ahead of the solid-liquid interface was about 5°C/mm and the solidification rates were 12, 6, 4, 2 and 1mm/hr. The specimens of 14mm diameter ×100mm long were melted and moved at the above mentioned constant speed through a vertical electric furnace.
The solidification interface of ledeburite eutectic was perturbed when the solidification rate was fast, but it became planar without primary cementite crystallization when the rate was slow. The primary cementite section was characteristically “ L-shaped ”. This cementite which was located at the center and/or boundary of eutectic structure controlled the growth direction of eutectic lamellae. At slow solidification rates, ledeburite lamellae were aligned by the decrease of lamellar faults.
Inter-lameller spacing λ changed with the relation of λ=A⋅Rn, where R is the solidification rate, and A and n are constants. In the present investigation, n was estimated to be apout −1/3 for Fe-C-C1 alloy.
