Time Evolution of Solidification Structure in Ductile Cast Iron with Hypereutectic Compositions
Time Evolution of Solidification Structure in Ductile Cast Iron with Hypereutectic Compositions
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过共晶成分球墨铸铁凝固组织的时间演化
DOI：
10.1007/s40962-020-00424-3
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
H. Yasuda
中科院分区：
文献类型：
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作者：
Kiattisaksri Chatcharit;A. Sugiyama;K. Morishita;T. Narumi;K. Kajiwara;H. Yasuda
利用同步辐射装置SPring-8（日本兵库县）BL20XU的x射线（二维观察）和时间分辨断层扫描（三维观察）原位观察了添加镁后球墨铸铁的显微组织演变。在二维观察中，石墨结核在熔体中成核，成核后立即上浮。石墨结核被吞没到奥氏体枝晶中，从而终止了浮力。x线摄影显示，100 μm厚的试样中，平均悬浮距离小于枝晶臂间距。由于短距离可能受到样品约束的影响，因此在SPring-8的BL28B2中使用粉红色x射线束进行时间分辨层析成像。在熔体中成核的石墨结核（可能在熔体中的镁-氧-硫包裹体上）在几秒钟内漂浮并被奥氏体枝晶吞没，即使在大块样品中也是如此。虽然体积试样的平均距离约为100 μm厚试样的两倍，但两种方法均能在短时间内观察到形核后的漂浮和吞没到奥氏体枝晶中。成核和包裹顺序对石墨结核的数量和大小有重要影响。
The microstructure evolution in ductile cast iron with magnesium addition was observed in situ by using X-ray radiography (two-dimensional observation) and time-resolved tomography (three-dimensional observation) in the BL20XU of a synchrotron radiation facility, SPring-8 (Hyogo, Japan). In the two-dimensional observation, graphite nodules nucleated in the melt and floated up immediately after nucleation. The floating was terminated by engulfment of graphite nodules into austenite dendrites. The radiography indicated that the average floating distance was shorter than the dendrite arm spacings in the 100-μm-thick specimen. Because the short distance could be influenced by the sample confinement, time-resolved tomography was performed by using a pink X-ray beam in the BL28B2 of SPring-8. Graphite nodules that nucleated in the melt (probably on magnesium–oxygen–sulfur inclusions in the melt) floated and were engulfed by austenite dendrites within several seconds, even in the bulk specimen. Although the average distance in the bulk specimen was approximately twice as large as that in the 100-μm-thick specimen, floating after nucleation and engulfment into austenite dendrites within a short duration were observed commonly from both techniques. The sequence of nucleation and engulfment had a critical effect on the number and size of the graphite nodules.