Evolution of semi-solid structure of hypoeutectic white cast iron by rheocasting

The evolution of semi-solid structure of hypoeutectic white cast iron ingots containing 2.5% carbon and 1.8% silicon was investigated by rheocasting. The solidifying alloys were vigorously agitated by electromagnetic stirrer during isothermal and continuous cooling processes. The experiment result showed that at proper agitating temperatures and speed, the dendrite structures were gradually evolved into global semi-solid structures after stirred for a certain time. The isothermal agitating was processed at two different temperatures, one is at 1523K, which was 20K lower than the temperature of liquidus of the alloy, and the other is at 1483K, which was 54K higher than the solidus of the alloy. During the isothermal process, the dendrites were bent by convection, the secondary dendrites separated from the primary ones, and finally, the dendrites changed gradually into granular structures. In particular, grains clustering were observed in the microstructures of the alloy when isothermal temperature or agitating speed decreased abruptly. More dendrite fragments can be obtained than the former in continuous cooling process by electromagnetic agitating process.