Dendrite morphology of steady state unidirectionally solidified steel

Abstract

Steady state directional freezing experiments have been performed with two steels containing 0.59 and 1.48 pct carbon. Primary and secondary arm spacings were directly measured. In addition, average primary arm spacings were computed from the number of arms present on the observed area using the model of a hexagonal arrangement. The latter method seems to be more objective and reproducible than the line counting method. Arm spacings λ were related by the empirical equation λ =c R ^mGⁿ to growth rateR and temperature gradientG. For primary arms, the exponentsm andn were different, whereas for secondary arms they were almost identical. Some consideration is given to dendrite spacings in ingot solidified steel, where under parabolic growth conditions thermal gradients and growth velocity are coupled by heat flow. Hence, a single variable may be used if the boundary condition for heat flow remains the same. Using the present results the laws describing dendrite spacings as a function of local solidification time are derived and compared with previous data available in the literature.