Low-velocity growth in laser resolidified Fe-C-Si alloys

Laser remelting experiments at 50 and 100 mu m/s scanning velocity were emp loyed to study the microstructure in Fe-C-Si alloys with compositions in th e range: 3.2-4.2 wt.% C and 1-3 wt,% Si. Due to the geometry of the liquid pool, different growth velocities were obtained during remelting; zero at t he bottom of the pool and a rate close to the laser velocity near the surfa ce. Solidification starts with gray iron with vermicular graphite morpholog y and changes to a white ledeburitic structure near the surface. The measur ed velocity for the gray-white transition was about 43 mu m/s for all analy zed alloys. Theoretical models show that this transition velocity is highly sensitive to the Si-content in the alloy, which was not verified by the ex periments. Changes in composition of C and Si during processing explain the observed disagreement between experimental results and theory.