Abstract
The temperature of eutectic growth front was measured in unidirectionally solidifying Fe-C-Cr eutectic cast irons. In cast irons containing Cr 0.3% and 0.5%, flake graphite eutectic grows at low growth rates and ledeburite eutectic grows at the rate about 1μm/sec or more. Flake graphite eutectic and ledeburite eutectic simultaneously grow at the rate where the transition from flake graphite eutectic to ledeburite eutectic solidification occurs. Undercooled graphite eutectic often appears in 0.3% Cr cast iron instead of ledeburite eutectic at high growth rates. Graphite eutectic appears neither in 1% nor 2% Cr cast iron. Ledeburite eutectic grows at higher temperature than the undercooled graphite eutectic. The temperature depression of ledeburite eutectic is linear to the square root of the growth rate in the range of high growth rate at which the solid-liquid interface of the eutectic is of well-developed cellular structure. The equilibrium ledeburite eutectic temperature rises and the equilibrium austenite-graphite temperature falls with an increase of Cr content. The transition from flake graphite eutectic to ledeburite eutectic solidification is well explained in terms of the relationship between the growth temperature and the growth rate. Chromium has such effects as facilitating nucleation of ledeburite eutectic and raising the ledeburite eutectic temperature on the transition.
