过共晶球铁中奥氏体枝晶形貌分析

Morphology Analysis of Austenitic Dendrite in the Hypereutectic Ductile Iron

采用着色腐蚀金相显示球铁中奥氏体枝晶，借助扫描电镜观察球铁缩松区形貌，研究了过共晶球铁中奥氏体枝晶形貌特征、分类及形成条件。结果表明，过共晶球铁中奥氏体枝晶具有典型三维空间结构，可分两种类型，即初生枝晶和晕圈枝晶。过冷度是影响枝晶析出的显著性因素，铸件模数ＭＣ增加，枝晶数量减少，形态趋于不发达，由初生枝晶向晕圈枝晶过渡。

The austenitic dendrites in hypereutectic ductile iron are showed using coloration etching,the morphology of shrinkage porosity in ductile iron is observed by the use scanning electron microscope,hence the morphology,classification and formation conditions of austenitic dendrites in hypereutectic ductile iron have been studied.The results revealed that the austenitic dendrites in hypereutectic ductile iron have typical three dimentional structure,which can be divided into two types,namely austenitic primary dendrite and austenitic shell dendrite.The degree of undercooling is a remarkable factor influencing the precipitation of austenitic dendrites,with increasing the casting modulus M C counts of dendrites are reduced, the morphology of dendrites in hypereutectic ductile iron will be transformed from primary austenitic dendrite into shell dendrite.