球墨铸铁离异共晶凝固组织生长模拟

摘要：采用所开发的微观元胞自动机模型，耦合热力学模型计算获得的凝固路径，将浓度分布、温降与晶体生长相结合，模拟了亚共晶球墨铸铁(Fe-4wt%C合金)离异共晶组织生长过程。结果表明，奥氏体与石墨生长相互促进，奥氏体晶粒快速包裹石墨，生长形态由枝晶状转为团簇状，石墨晶粒最终孤立分布于奥氏体基体中。等温下仅依靠溶质扩散的奥氏体与石墨生长速度略低于温降和溶质扩散共同作用下数值。二者生长速度随熔体初始过冷度增大均增快；随冷却速率增加均呈线性增长，增幅大致相同。本计算参数范围内，冷却速率对石墨生长速度的影响强度大于熔体初始过冷度。所预测的石墨平均半径与文献实验值相符。研究结果可为控制球墨铸铁凝固组织形貌及性能提供依据。

Simulation of divorced eutectic microstructure evolution in ductile iron solidification process

A microscopic cellular automaton model for binary alloy,coupled with the solute concentration distribution,temperature decrease and grain growth,was developed to simulate the divorced eutectic microstructure evolution in a hypoeutectic ductile iron (Fe-4wt%C alloy) solidification process.The results show that the austenite and graphite grains grow in a mutually promotive way.The morphology of the austenite grain alters from dendritic to cluster like once it touches and then envelopes the graphite grain, which makes the graphite grains distribute isolatedly in the austenite matrix in its final microstructure.It is also shown that the growth rates of the austenite and graphite grains under isothermal condition are slightly lower than the ones with the contribution of both the temperature decrease and solute diffusion.Both the growth rates of austenite and graphite grains rise up with the increase of the initial undercooling of the melt, and increase linearly with the cooling rate ranged within -5—-30K/s.The amplitude of the growth rate increasing with the cooling rate in the direction of austenite dendrite arm is almost the same as that of the graphite.Under the present calculation condition, the influencing intensity of the cooling rate on the growth rate of the graphite grains is greater than the initial undercooling of the melt.The predicted average radius of the graphite grains, 11.82μm, fits with the measured data in the literature, 14.71μm.The results are helpful for the control of the solidification microstructure and the properties of the ductile irons.