流变铸造亚共晶白口铸铁组织结构的演变

利用电磁搅拌方法研究了亚共晶白口铸铁半固态浆料凝固组织的演变。结果表明，在等温搅拌过程中，球形颗粒半固态组织的形成是一种渐变过程，经历了一次枝晶和二次枝晶的分离、枝晶的弯曲和粒化阶段，搅拌温度、激磁电流和搅拌时间三者恰当的配合会导致为理想的球形颗粒组织，由温度降低造成的搅拌力或搅拌速度的突然降低导致颗粒簇聚的现象。在连续冷却过程中，流变铸造组织出现了枝晶断裂迹象，而在等温过程中则较少见。

EVOLUTION OF MICROSTRUCTURES OF HYPOEUTECTIC WHITE CAST IRON INGOTS BY RHEOCASTING

An investigation was made on the evolution of microstructures of hypoeutectic white cast iron ingots containing 2.5% carbon and 1.8% silicon produced by rheocasting in which the solidifying alloys were vigorously agitated by electromagnetic stirrer during isothermal cooling and continuous cooling processes. Results showed that for proper agitating temperatures and speed, dendrite structures were gradually evolved into global structures for certain agitating time. In fact, the isothermal cooling process can be divided into two stages, i.e. 1523K which was 20K lower than the temperature of Iiquidus of the alloy and 1483K which was 54K higher than the solidus of the alloy. It was obvious that the dendrites were being bent by convection or formed by bend growth of the dendrites themselves and gradually being changed into separated particles and into more global structures in the end during isothermal cooling process. 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.