过共晶球墨铸铁中石墨球周围奥氏体壳的形成机制

摘要

The high-temperature solidification structure in hypereutectic nodular iron has been showed clearly by the color etching technique and the formation mechanism of the austenite shell （the austenite shell is a part of the austenite dendrites） around the nodular graphite has been observed and analyzed. The result shows that the primary austenite dendrite and austenite shell dendrite grows alternately through the primary nodular graphite, this helps to bring about the formation of the austenite shell around nodular graphite. Around the primary nodular graphite, the austenite nucleates and grows based on the graphite growth face (0001), and forms a ring like austenite shell finally. At the earlier stage of eutectic, the graphite nodules nucleate and grow between dendrites arm or in the frame of the austenite dendrites, then are surrounded by the austenite dendrite arms formed later, finally the enveloped or nor-enveloped frame austenite shell has formed. But, There is no austenite shell formed around the nodular graphite formed in the later stage of eutectic.%采用着色腐蚀技术，可清晰地显示出过共晶球墨铸铁中的高温凝固组织，观察分析了石墨球周围奥氏体壳（奥氏体壳是奥氏体枝晶的一部分）的形成机制。结果表明，初生枝晶和晕圈枝晶交替生长，促成石墨球周围奥氏体壳的形成；奥氏体以石墨生长面（0001）为衬底形核、生长，在初生石墨球周围形成环状封闭奥氏体壳；共晶前期石墨球在枝晶臂间或框架中形核、生长，尔后为枝晶高次臂所包围，形成封闭或不封闭的框架奥氏体壳。共晶后期石墨球不形成奥氏体壳。