Morphological instability of the austenite growth front in a laser remelted iron-carbon-silicon alloy

Growth morphology transitions of austenite during solidification of a laser remelted Fe-C-Si alloy have been studied by theoretical modeling and laser remelting experiments. A synthetic cast iron with 1.7 wt% C and 4.3 wt% Si was remelted using laser scanning velocities ranging from 5 x 10(-5) to 2 x 10(-1) m/s. Three different austenite morphologies have been found: plana r, cellular and dendritic. A transition from planar to cellular solid/liqui d interface of the austenite crystals is observed at a solidification veloc ity of 30 mu m/s. Another morphological transition between cells and dendri tes is observed at 1.5 mm/s growth velocity. The experimental results of tr ansition velocities have shown good agreement with theoretical values. The primary dendrite spacing in the laser remelted zone is also evaluated and c ompared with the theoretical predictions. (C) 2000 Published by Elsevier Sc ience B.V. All rights reserved.