Abstract
The temperature of eutectic growth front in unidirectionally solidified cast irons and their graphite structure were investigated in the range of growth rate from 0.32 to 25μm/sec. The eutectic growth temperature was lowered by increasing growth rate, and raised by increasing silicon content. The eutectic with coarse flake graphite grew at low growth rates, whereas fine undercooled graphite eutectic structure appeared at high growth rates. The transition of coarse flake-fine undercooled graphite structure occured at growth rates around 4μm/sec and almost independent of silicon content. The equillibrium eutectic temperature rose linearly with the silicon content at the rate of 3.2°C per percent silicon from 1,154.5°C of pure iron-carbon eutectic temperature. The undercooling of the eutectic growth front was nearly proportional to the square root and cube root of the growth rate in coarse flake graphite and in fine undercooled graphite structure. The transition of coarse-fine undercooled graphite structure was explained in terms of the relationship between the eutectic growth temperature and growth rate.
